Using more *::Constants::ICON_* where it makes sense and
wrapping the file names into QLatin1String where they were
missing.
The increased usage of the ICON constants needed a few more
cross plugin includes of *constants.h, here and there.
I think that it is OK, since the dependencies were alredy there
icon resource wise.
Since we use a two column model/treeview we need to prevent returning
some text data, otherwise we will see dots in the secound column. We also
need to emit pagesChanged once we init the model.
