[qtmozembed] Cleanup startup sequence

- If mozcontext ready, view created on component completed.
- Creation of render object connected to beforeSynchronizing, no
  need anymore for scenegraph initialized connection. The beforeSynchronizing
  is also good in sense that the GUI thread is locked.
- Due to above GL context used for rendering is bound and QSGThreadObject
  could be made self-contained.
Cleanup NO_PRIVATE_API ifndef blocks and related sources
Merge pull request #79 from rainemak/removeNoPrivateApi

Clean NO_PRIVATE_API usage