Merge pull request #3493
9a2305a qt: Stop shutdown detection timer during shutdown (Wladimir J. van der Laan)
35ecf85 qt: Remove global references in bitcoin.cpp (Wladimir J. van der Laan)
55fe4de qt: Show window while shutting down (Wladimir J. van der Laan)
202d853 qt: Move initialization/shutdown to a thread (Wladimir J. van der Laan)