cmake: Just check whether .git exists

When the source tree is a git submodule (for example when it is in
hawaii.git) ".git" is a file not a directory so we just check whether it
exists or not.
declarative: Don't set client rendering and don't enable touch events

Compositors will do it.
Update year in copyright notice
Add git files
Bump version to 0.2.90
Simpler window wrapper

Add a couple of simpler QML window wrappers for surface items and move
the unresponsive logic to the client window wrapper.
libgreenisland: Remove Compositor::surfaces()

It's already in QWaylandCompositor.
libgreenisland: Send frame callbacks at the right time
libgreenisland: Move SurfaceItem here
libgreenisland: Fix typo in signal connection

Missing parenthesis in slot.
Bump version to 0.3.0