Re-establish behavior where any slave deck rate change can affect master.
Clean up, unify naming a little.
Use qFuzzyCompare for float comparisons.
Only create one QApplication (in GUI-mode) per mixxx-test run.
Minor optimization to BeatGrid::findNthBeat.
Merge remote-tracking branch 'mixxx/master'
Merge branch 'master' into master_sync
Merge branch 'master_sync' of github.com:mixxxdj/mixxx into master_sync

Conflicts:
	src/engine/bpmcontrol.cpp
	src/test/mockedenginebackendtest.h