This merges the first part of the mvc refactoring: it makes
Calligra use xmlgui directly instead of kparts. We weren't
using kparts for what they were intended for, that is, embedding
a combined document/view object into some container.

Now KoPart is factory for views and mainwindows. KoDocument handles
all loading/saving internally.

Next up: make KoPart and KoMainWindow manage multiple views and
documents.

REVIEW:111545

Conflicts:
	krita/ui/kis_view2.cpp
	krita/ui/widgets/kis_workspace_chooser.cpp
	libs/main/CMakeLists.txt
	libs/main/KoDocument.h
	libs/main/KoMainWindow.cpp
	libs/main/KoMainWindow.h