Ensure item position is valid
Support Cmd+H for hide on OSX

cherry-picked from:
* https://github.com/plexinc/plex-home-theater-public/commit/f7718f453 (CApplication changes)
* https://github.com/plexinc/plex-home-theater-public/commit/7ce72ca9f (CApplicationMessenger changes)
* https://github.com/plexinc/plex-home-theater-public/commit/0e23c8312 (WinEventsSDL changes)
Remove Python dialogs when compiling without Python

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/f76df3e72
Use extension to set MIME type for internet streams, if possible

cherry-picked from:
* https://github.com/plexinc/plex-home-theater-public/commit/cca576470
* https://github.com/plexinc/plex-home-theater-public/commit/f27fe1b33
Have CGUIInfoManager::GetWindowWithCondition() handle a window ID of 0 (fixes annoying posy changes)

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/a1caa3bc6
CTextureCacheJob: Hash the URL instead of stat'ing an internet stream

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/778550c32
Workaround for what appears to be a bug in the Windows heap

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/b36f9672e