[libngf-qt] Client: emit eventPlaying() on play()

Relates NEMO#684
Use qmake variable to deal with the -qt5 suffix

Relates NEMO#684
Add configure() qmake function

Relates NEMO#684
[tests] Initial commit

Relates NEMO#684
Do not set OBJECTS_DIR & MOC_DIR qmake variables

Using variables like these makes usage of 'lcov' coverage analyzis tool
impossible. Please consider using qmake's support for shadow building
instead:

  cd build/ && qmake .. && make

Relates NEMO#684
Add 'coverage' make target

Relates NEMO#684