...to better be able to change its set of implemented interfaces later on.

Some potential for further clean up:
* a generic helper for supportsService;
* remove need for impl_createFactory;
* base impl_createInstance on XComponentContext instead of XMultiServiceFactory;
* replace ThreadHelpBase with a plain osl::Mutex.

Change-Id: Ia2cbd14872a609c2ed57d9ce58b546f087c2fdfb