Kill scoped_ptr in favor of unique_ptr
Extract ColorValidator from Automation's dialog stuff
Use ColorValidator in DialogStyleEditor
Make libass a hard dependency

There's really no point in letting people build Aegisub without any
subtitle renderers.
Remove handling for no subtitle providers available
Fix setting the style editor preview background color
Remove a bunch of cruft from the configure script
Drop support for non-little-endian platforms

Aegisub doesn't actually currently run on any.
More unique_ptr
Fix crash when opening non-cached audio
Update the title of the detached video dialog when videos are opened. Closes #1607.
Simplify clipboard_set slightly
Change some enums into enum classes
Slightly simplify DialogVideoDetails
Clean up DialogJumpTo slightly
Remove some unused includes in video_box.cpp