Add app templates for meson c and c++ project

Will add two new items under:

 Project -> New from Template

When Standard -> Terminal is chosen the user now has two added options in the drop down menu: Meson c project or Meson c++ project.

Also, add file containing SPDX license information.

.reuse/dep5

+Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
+Upstream-Name: KDevelop
+Upstream-Contact: KDE Community
+Source: https://invent.kde.org/kdevelop/kdevelop
+
+Files: app_templates/c/meson/meson_plainc/*
+Copyright: Morten Danielsen Volden <mvolden2@gmail.com>
+License: LGPL-2.1-or-later
+
+Files: app_templates/cpp/meson/meson_plaincpp/*
+Copyright: Morten Danielsen Volden <mvolden2@gmail.com>
+License: LGPL-2.1-or-later

app_templates/CMakeLists.txt

@@ -3,9 +3,11 @@ kdevplatform_add_app_templates(
     cpp/CMake/cmake_qt5guiapp
     cpp/CMake/cmake_kdevplugin
     cpp/CMake/cmake_qt5-qml2
+    cpp/meson/meson_plaincpp
     cpp/QMake/qmake_qt5guiapp
     cpp/QMake/qt5-qml2
     c/CMake/cmake_plainc
+    c/meson/meson_plainc
     empty
     kdevelop/file_template_template
 )

app_templates/c/meson/meson_plainc/%{PROJECTDIRNAME}.kdev4

+[Project]
+CreatedFrom=meson.build
+Manager=KDevMesonManager
+Name=%{APPNAME}
+

app_templates/c/meson/meson_plainc/main.c

+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char *argv[])
+{
+    puts("Hello, World!");
+    return 0;
+}

app_templates/c/meson/meson_plainc/meson.build

+project(
+    '%{APPNAMELC}',
+    'c',
+    version : '1.0.0',
+    default_options : [
+        'buildtype=debug',
+        'optimization=0',
+        'c_std=c17'
+    ],
+    meson_version: '>= 0.60.0',
+)
+
+
+executable('%{APPNAMELC}',
+           'main.c'
+)
+

app_templates/c/meson/meson_plainc/meson_plainc.kdevtemplate

+# KDE Config File
+[General]
+Name=Meson C
+Comment=Simple Meson-based C application
+Category=Standard/Terminal
+Icon=default-kdevelop
+ShowFilesAfterGeneration=main.c
+ValidProjectName=^[a-zA-Z_][a-zA-Z0-9_-]+$

app_templates/cpp/meson/meson_plaincpp/%{PROJECTDIRNAME}.kdev4

+[Project]
+CreatedFrom=meson.build
+Manager=KDevMesonManager
+Name=%{APPNAME}
+

app_templates/cpp/meson/meson_plaincpp/main.cpp

+#include <iostream>
+
+int main(int argc, char **argv) {
+    std::cout << "Hello, world!" << std::endl;
+    return 0;
+}

app_templates/cpp/meson/meson_plaincpp/meson.build

+project(
+    '%{APPNAMELC}',
+    'cpp',
+    version : '1.0.0',
+    default_options : [
+        'buildtype=debug',
+        'optimization=0',
+        'cpp_std=c++17'
+    ],
+    meson_version: '>= 0.60.0',
+)
+
+
+executable('%{APPNAMELC}',
+           'main.cpp'
+)
+

app_templates/cpp/meson/meson_plaincpp/meson_plaincpp.kdevtemplate

+# KDE Config File
+[General]
+Name=Meson C++
+Comment=Simple Meson-based C++ application
+Category=Standard/Terminal
+Icon=default-kdevelop
+ShowFilesAfterGeneration=main.cpp
+ValidProjectName=^[a-zA-Z_][a-zA-Z0-9_-]+$