Enable modularization of translation files.

Enable modularization of translation files.

This is accomplished by introducing dependencies to catalogs.

This requires one API change:
QTranslator::load(const uchar *, int);
  changes to
QTranslator::load(const uchar*, int len,
                  const QString &directory = QString());

Since now, even the load from memory might need a directory if
the memory block contains a qm file with dependencies.

Change-Id: I781f333d07f53bb431d0a7b5fa1abe282dc4d338
Task-number: QTBUG-26138
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>