Fix the remaining include directives to follow Qt conventions

In public header files, always use this form to include Qt
headers: #include <QtCore/qwhatever.h>. The library prefix
is very convenient for non-qmake projects.

Change-Id: I033ae9defee2ae7d383d8f268a4d7923162ac49e
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>
Reviewed-by: Caroline Chao <caroline.chao@digia.com>