Center axes, make them thicker
Change SoundRecorder microphone icon background

Fixes #692.
* Background of the SoundRecorder is now transparent, thus matches the background color of the rest of the app.
* Renamed icons to match our naming scheme.
Merge pull request #762 from Catrobat/issue#684

[Catroid]draw thicker axes
Merge pull request #778 from Catrobat/issue#692

Change SoundRecorder microphone icon background
Merge branch 'master' into issue#665
changed testBackButtonPressedTwice