IcuTranslatorFactory: make castable to TranslatorFactory
IcuTranslatorFactory: make castable to TranslatorFactory

Fixes: 20a9d4692f43 ("IcuTranslator: new class")
Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server