- Moved all platform-specific code to UBPlatformUtils
- For now, removed support (on Linux) for checking whether onboard is 
running when OpenBoard is started (it wasn't working anyway, but it needs a
cleaner solution for all 3 platforms)

Due to QWidget::showFullScreen having side-effects on OSX (setting the
dock and menubar to autohide, making it impossible to then set them as
hidden), the calls to that method were replaced with
UBPlatformUtils::showFullScreen(QWidget *). This function then calls
QWidget::showMaximized() on OSX, or QWidget::showFullScreen() on Linux
and Windows.

It is currently still impossible to switch smoothly between showing or
hiding the dock on OSX; current behaviour is to hide it all the time,
even in desktop mode.

removed redundant OBCocoa files / namespace; moved functions to UBPlatformUtils, which serves the same purpose

Changing the languages of the virtual keyboard crashes the software

No swiss-french in virtual keyboard in Ubuntu

fixed issue SANKORE-574 and font manager is now translated depending on the system lanaguage (linux only but other will be fixed soon too) and some script build issues fixed on linux