Use consistent button which is flat on mobile devices

src/qml/LoginPage.qml

@@ -35,6 +35,8 @@ import QtQuick.Layouts 1.3
 import org.kde.kirigami 2.8 as Kirigami
 import im.kaidan.kaidan 1.0
 
+import "elements"
+
 Kirigami.Page {
 	title: qsTr("Log in")
 
@@ -92,7 +94,7 @@ Kirigami.Page {
 			}
 
 			// Connect button
-			Controls.Button {
+			Button {
 				id: connectButton
 				Layout.fillWidth: true
 				highlighted: true

src/qml/elements/Button.qml

+/*
+ *  Kaidan - A user-friendly XMPP client for every device!
+ *
+ *  Copyright (C) 2016-2019 Kaidan developers and contributors
+ *  (see the LICENSE file for a full list of copyright authors)
+ *
+ *  Kaidan is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  In addition, as a special exception, the author of Kaidan gives
+ *  permission to link the code of its release with the OpenSSL
+ *  project's "OpenSSL" library (or with modified versions of it that
+ *  use the same license as the "OpenSSL" library), and distribute the
+ *  linked executables. You must obey the GNU General Public License in
+ *  all respects for all of the code used other than "OpenSSL". If you
+ *  modify this file, you may extend this exception to your version of
+ *  the file, but you are not obligated to do so.  If you do not wish to
+ *  do so, delete this exception statement from your version.
+ *
+ *  Kaidan is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with Kaidan.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import QtQuick.Controls 2.4 as Controls
+import org.kde.kirigami 2.8 as Kirigami
+
+/**
+ * This is a button fitting mobile and desktop user interfaces.
+ */
+Controls.Button {
+	flat: Kirigami.Settings.isMobile
+}

src/qml/elements/RosterAddContactSheet.qml

@@ -91,7 +91,7 @@ Kirigami.OverlaySheet {
 		RowLayout {
 			Layout.topMargin: 10
 
-			Controls.Button {
+			Button {
 				text: qsTr("Cancel")
 				onClicked: {
 					clearInput()
@@ -100,7 +100,7 @@ Kirigami.OverlaySheet {
 				Layout.fillWidth: true
 			}
 
-			Controls.Button {
+			Button {
 				id: addButton
 				text: qsTr("Add")
 				enabled: {

src/qml/elements/RosterRemoveContactSheet.qml

@@ -61,13 +61,13 @@ Kirigami.OverlaySheet {
 			Layout.topMargin: 10
 			Layout.fillWidth: true
 
-			Controls.Button {
+			Button {
 				text: qsTr("Cancel")
 				onClicked: close()
 				Layout.fillWidth: true
 			}
 
-			Controls.Button {
+			Button {
 				text: qsTr("Delete")
 				onClicked: {
 					kaidan.removeContact(jid)

src/qml/elements/RosterRenameContactSheet.qml

@@ -57,13 +57,13 @@ Kirigami.OverlaySheet {
 		RowLayout {
 			Layout.topMargin: 10
 
-			Controls.Button {
+			Button {
 				text: qsTr("Cancel")
 				onClicked: close()
 				Layout.fillWidth: true
 			}
 
-			Controls.Button {
+			Button {
 				id: addButton
 				text: qsTr("Rename")
 				onClicked: {

src/qml/elements/SendMediaSheet.qml

@@ -114,7 +114,7 @@ Kirigami.OverlaySheet {
 			Layout.topMargin: Kirigami.Units.largeSpacing
 			Layout.fillWidth: true
 
-			Controls.Button {
+			Button {
 				text: qsTr("Cancel")
 
 				Layout.fillWidth: true
@@ -125,7 +125,7 @@ Kirigami.OverlaySheet {
 				}
 			}
 
-			Controls.Button {
+			Button {
 				id: sendButton
 
 				enabled: root.source != ''

src/qml/elements/SubRequestAcceptSheet.qml

@@ -56,7 +56,7 @@ Kirigami.OverlaySheet {
 		RowLayout {
 			Layout.topMargin: 10
 
-			Controls.Button {
+			Button {
 				Layout.fillWidth: true
 				text: qsTr("Decline")
 				onClicked: {
@@ -65,7 +65,7 @@ Kirigami.OverlaySheet {
 				}
 			}
 
-			Controls.Button {
+			Button {
 				Layout.fillWidth: true
 				text: qsTr("Accept")
 				onClicked: {

src/qml/qml.qrc

@@ -21,6 +21,7 @@
 		<file>elements/ChatMessage.qml</file>
 		<file>elements/RoundedImage.qml</file>
 		<file>elements/RoundImage.qml</file>
+		<file>elements/Button.qml</file>
 		<file>elements/IconButton.qml</file>
 		<file>elements/FileChooser.qml</file>
 		<file>elements/FileChooserDesktop.qml</file>

src/qml/settings/ChangePassword.qml

@@ -34,6 +34,8 @@ import QtQuick.Layouts 1.3
 import org.kde.kirigami 2.8 as Kirigami
 import im.kaidan.kaidan 1.0
 
+import "../elements"
+
 Kirigami.Page {
 	topPadding: 0
 
@@ -117,13 +119,13 @@ Kirigami.Page {
 			Layout.fillWidth: true
 			Layout.alignment: Qt.AlignBottom
 
-			Controls.Button {
+			Button {
 				text: qsTr("Cancel")
 				onClicked: stack.pop()
 				Layout.fillWidth: true
 			}
 
-			Controls.Button {
+			Button {
 				text: qsTr("Change")
 				Layout.fillWidth: true
 				enabled: {