Move stuff around to make it easier to have a harmattan frontend

mobile/plugins/widgets/CMakeLists.txt

-install( FILES
-	Button.qml CalcButton.qml CategoryDelegate.qml ConsoleDelegate.qml ExpressionInput.qml
-	Keyboard.qml RealInput.qml ToolTip.qml SimpleListView.qml
-	
-	KAlgebraPage.qml  KAlgebraMobile.qml
-	DESTINATION ${DATA_INSTALL_DIR}/kalgebra/plugins/widgets/
-)
+option(MOBILE_BACKEND "backend to install, currently desktop and harmattan (directories in this folder)" "desktop")
+if(NOT MOBILE_BACKEND)
+    set(MOBILE_BACKEND "desktop")
+endif(NOT MOBILE_BACKEND)
+
+add_subdirectory(${MOBILE_BACKEND})
\ No newline at end of file

mobile/plugins/widgets/desktop/CMakeLists.txt

+install( FILES
+    Button.qml CalcButton.qml CategoryDelegate.qml ConsoleDelegate.qml ExpressionInput.qml
+    Keyboard.qml RealInput.qml ToolTip.qml SimpleListView.qml
+    
+    KAlgebraPage.qml  KAlgebraMobile.qml
+    DESTINATION ${DATA_INSTALL_DIR}/kalgebra/plugins/widgets/
+)