[qtmozembed] WIP: Drop private API usage

TODO:
- All NO_PRIVATE_API blocks should be dropped
- init() and initialize() should be combined (didn't do yet, so that diff is clearer)
- Rename onInitialized to something like onContextInitialized
Merge pull request #78 from rainemak/dropPrivateAPIUsage

[qtmozembed] WIP: Drop private API usage