Detach common.pri from the nano browser examples.

Move common.pri to the root directory to be able to use it with tests.
Remove nano browser specific logic (util.h include and common resources)
from this file and use relative paths in the examples instead.

This also remove unnecessary directives:
- lib doesn't have to be added to INCLUDEPATH since proper modules are used
- util.h doesn't need to be added to HEADERS, moc doesn't need to go through it
- MOC_DIR doesn't have to be adjusted anymore

Change-Id: Id706e7f2ef7c9607bdcd0ba63afecf5b5854262b
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>