New: Add window group class managing plugins' QWindows.
New: Add window group class managing plugins' QWindows.

RevBy: Jan Arne Petersen

That class takes over AbstractSurfaceGroup's duties. It makes sure that QWindows
are hidden, when plugin is deactivated and notifies about changes in input
method area. It also sets some useful window flags.

Later it can setup wayland input method communication.

Also, added a Malit::Position enum, which can be later used by WindowGroup class
to tell compositor where it should place the input method surface.

Full, original commit at 91ab7f504b260c5cf3b21a2613e8fabd75f1a1cf in maliit-framework

perencia/inputcontext-qt4,maliit/inputcontext-qt4,maliit/inputcontext-qt4