QCoreApplication - add return type bool on install/remove translator

QCoreApplication - add return type bool on install/remove translator

This add a bool as return value on QCoreApplication::installTranslator
and QCoreApplication::removeTranslator. It returns true on success.

Before it was very clumsy to detected this. It was needed to react
on the signal and mark a success - just to provide an error message
on failure.

This is 99.99% source compatible - only if someone grabs a function
pointer to this - it will break the code - but it seems to be very
theoretic.

Change-Id: I947fcee1352f530e559bb177a90c10d84eed1aec
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>