Move scenes to the src directory

Similar to the backends, it's far more intuitive to have scenes in the
toplevel source directory rather than the plugins directory.

src/CMakeLists.txt

@@ -230,6 +230,7 @@ target_link_libraries(kwin
 )
 
 add_subdirectory(backends)
+add_subdirectory(scenes)
 
 if (KWIN_BUILD_CMS)
     target_sources(kwin PRIVATE

src/Messages.sh

@@ -1,3 +1,3 @@
 #! /usr/bin/env bash
 $EXTRACTRC *.kcfg *.ui >> rc.cpp
-$XGETTEXT *.h *.cpp plugins/nightcolor/*.cpp helpers/killer/*.cpp plugins/scenes/opengl/*.cpp tabbox/*.cpp scripting/*.cpp plugins/krunner-integration/*.cpp -o $podir/kwin.pot
+$XGETTEXT *.h *.cpp plugins/nightcolor/*.cpp helpers/killer/*.cpp scenes/opengl/*.cpp tabbox/*.cpp scripting/*.cpp plugins/krunner-integration/*.cpp -o $podir/kwin.pot

src/plugins/CMakeLists.txt

@@ -1,7 +1,6 @@
 add_subdirectory(kglobalaccel)
 add_subdirectory(qpa)
 add_subdirectory(idletime)
-add_subdirectory(scenes)
 add_subdirectory(windowsystem)
 add_subdirectory(kpackage)
 if (KWIN_BUILD_CMS)