core, add support to display the Qt version

It is the version of Qt we run with, not the one we compiled with.
core audio: removed autoplay property in our Audio item

This property is useless in our case and it create a bug on Android
with Qt5.4 only the first audio is played.
click_on_letter activity, no more play the audio on error

It is too confusing for children to have the wrong letter being
played when clicked. The children then forget what is expected.
numpad, no more steal mouse event when opaque

This fixes an issue in the scale activity where top left items was
not draggable due to the hidden NumPad.
fifteen activity, add support for keyboard

Now you can play the game with the keyboard instead of the mouse.
scale activity, fix a message in a question
core, no more start the intro music is effects are disabled

It makes sense to consider the intro music as being an effect and
not a voice even if we must push it to the voice channel to have it
played before the welcome voice.
minor, removed a useless import
gnumch activity, fix a message font size

We have not to ues the ratio when using pointSize because it is
already dpi adjusted by Qt.
fix a do/while crash and simplify the existing code
fix a do/while crash and simplify the existing code
Android: add splash screen
core: DownloadManager: register old rcc files upon download errors

... to avoid ending up without any voices upon network errors.

To achieve this we can't download directly into the local target rcc
files or we always overwrite the old ones. Therefore we  now download
into temporary files that are moved to the target files upon success.
Ported Braille Alphabets Activity in QML
Created BrailleChar and BrailleMap
Added current_alphabet function which returns current alphabet
braille_alphabets, fix copyright headers

Fix file naming to respect Qml convention.
braille_alphabet activity, minor code formating
braille_alphabets, major rework

Improved code and graphics.
Better layout, now scales well on different window ratio.
braille_alphabets, better BrailleChar.qml

Now BrailleChar.qml has the brailleChar property that represent
the text value of the char. It is possible to set the dots from
the char of set the char from the dots.