[Qt] update bitcoin-qt.pro and assets-attribution.md

- remove unused and unmentioned file notsynced.png (we use an animation
  for this)
- add missing coincontroldialog.ui to bitcoin-qt.pro
- also unify formating in assets-attribution.md
Upgrade gitian win32 to boost-1.55.

Fixes issue where all network activity just stops.
Merge pull request #3432

b960fcb [Qt] update bitcoin-qt.pro and assets-attribution.md (Philip Kaufmann)
Merge pull request #3503

0d512a9 gitian: Add -O2 for win32 build (Wladimir J. van der Laan)
Merge pull request #3501

56fce1f Upgrade gitian win32 to boost-1.55. (Warren Togami)
Merge pull request #3488

2102ab9 ui: Fix GUI initialization order (Wladimir J. van der Laan)
qt: Move initialization/shutdown to a thread

Move AppInit2 and Shutdown to a thread.

This allows a more responsive splash screen, prevents 'process does not respond'
messages from the window system and will allow for showing a user friendly
window while shutting down.
qt: Show window while shutting down

Makes it clear to the user that the application is still wrapping up
and the computer should not be turned off until it is finished.
qt: Remove global references in bitcoin.cpp

Remove the need for global references `guiref` and
`splashref` by making the BitcoinGUI and SplashScreen
classes register for the UI interface signals themselves.
qt: Stop shutdown detection timer during shutdown

Stop the shutdown timer from exiting the main loop
when shutdown is already in progress.

Fixes seeming hanging window after typing 'stop' in debug console.

Also hide the debug console during shutdown as it is useless without
a core to connect to.