Refactor window handling code

Currently when we want to show/raise the window in reaction to the tray icon/notification being clicked etc we do this by emitting a signal on the controller.
This is connected to in main.qml, which does some things, then calls back to controller to do more things.

This is quite convoluted. Instead introduce a new class WindowController that is responsible for all things window, in particular showing/raising and config saving

src/CMakeLists.txt

@@ -38,6 +38,7 @@ add_library(neochat STATIC
     joinrulesevent.cpp
     collapsestateproxymodel.cpp
     urlhelper.cpp
+    windowcontroller.cpp
 )
 
 add_executable(neochat-app