Install GCompris

Install GCompris executable and its runtimes dependencies.
Also install Qt and Qml runtime plugins.
The CMake fixup_bundle function is called to:
 - create a standalone executable bundle on OSX
 - copy GCompris dll dependencies on Windows

Add qt_helper.cmake module to ease Qt and Qml plugins installation.
Workaround fixup_bunle taking ages on Windows

For some reason (cmake bug ?), fixup_bundle on Windows takes age when giving
additional libraries. So do not fixup Qt and Qml plugins. Fixing up GCompris
seems to be enough anyway.
Adapted CMakeLists to linux
Corrected a problem between linux/osx plugins
Packaging .deb on Linux with CPack
Packaging .dmg on OSX with CPack

- customize Info.plist through MACOSX_BUNDLE_* target properties
- customize dmg background with the help of a manually created .DS_Store file
Package Linux: eventually use STGZ CPack generator
[FIX] also install QtGraphicalEffets
Copy/install translations to a subdirectory

Also copy .rcc files into the OSX bundle at build time.
Write .rcc files into a subdirectory
Corrected dmg missing Qt Framework
Hack for Qt5.3 since QtSvg is no more a cmake target
fix translations install
Put 5.3 as Qt Required version