Eliminate pointless wxDialog subclasses

A lot of the wxDialog subclasses don't actually override any virtual
functions, so there's no particular need for them to be subclasses at
all, and wxDialog's vtable is so huge that they actually contribute
measureable to the size of the executable.
Eliminate a bunch of entirely pointless OptionPage subclasses
Build wx without iostream support
Flush the clipboard before closing it, not after
Disable a bunch of ICU stuff we don't use

Bumps ~800KB off the executable (and 100MB off icu.lib).
Add a bunch of missing project references
Pull even more of the subs load logic into Project

The relative order of the on-file-load logic matters, so signals don't
work very well for it. Doing it all explicitly in Project fixes a bunch
of inconsistent issues related to restoring saved state.

Closes #1759.
Use the customized default styles for SRT files opened from matroska