Version and interface get passed to the ctor allowing Global::Private
to implement ::create instead of providing a pure virtual method.
Also the static bind method is added to the Global::Private which
delegates into a pure virtual method.
New base class KWayland::Server::Global which all Interface classes
for a wl_global inherit. Furthermore there is a shared base class
for all the Private classes of that type.
This implements the subcompositor and subsurface protocol on both
Client and Server side.
Client:
New classes SubCompositor and SubSurface. The SubCompositor can be
created through the Registry and creates the SubSurface which is
bound to a Surface and has a parent Surface. The SubSurface class
provides convenient wrappers for all calls exposed in the
wl_subsurface interface.
Server:
New classes SubCompositorInterface and SubSurfaceInterface. Support
for all commands is added, though the API probably still can need
some fine tuning. The synchronized vs. desynchronized behavior is
not yet exposed in the API. This could also be delegated towards
the user of the library.
