Fix planegame (report changes on Score.qml).
AudioFilePath for voices files depending on locale.
algebra_by, major rework

- improved images based on openclipart.org
- improved animation
- simplified code
core, minor added transparency on buttons.
added memory-math-add-minus-mult-div

Improved dataset for memory-math-div, memory-math-mult-div,
memory-math-mult.

Made Sound a common item instead of being on each card.
memory, cleanup removed useless files.
 Merge branch 'master' into 'master'

Fix planegame (problems with latest score.qml) + audio files
core: Bar: add repeat button
Ported click_on_letter activity

ToDo / Open Issues:

- Sound with qrc source schemes not working on Linux
(see https://bugreports.qt-project.org/browse/QTBUG-36e724).
- No voices sounds (on linux) unless symlinked manually.
- "fx"/sound settings faked by getSettings(), need settings
integration.
- No scaling on Linux because ApplicationInfo.ratio is never updated.
- Levels are statically initialized. Allow to initialize from file
(for non-latin locales), probably needs file IO support from C++.
- Flicking the train on Android can be improved.
algebra_by, improved text size

The new text size fit better on hdi screens.
findit, minor, improved text display.
core, minor, better display of the level.
core, minor better text size.
core, added a ParticleSystemStar

Replaced many particle star in several activities by a
new core ParticleSystemStar.
Merge remote-tracking branch 'upstream/master'