Turn on spell checking for YOSPOS

Autocorrection is probably all that needed to go away.  No spell checking is like posting in hard mode.
Made tweaks for autocorrection/etc forum level, not theme level

YOSPOS in a non-YOSPOS theme would have autocorrect
Fix for tweaks not being applied to thread composer
Fix for YOSPOS theme selection now changing…

Apparently keys with dashes in them aren’t saving in NSUserDefaults :psyduck:
Make list separators universally respect listSeparatorColor, made Settings theming more consistent with rest of app
Fix for migration running every startup + use setThemeName: forForumId: in migration instead of manually setting theme values
Change migration to not need additional key and clean up old keys
Cleaned up old settings defaults
Moved theming to viewWillAppear so refreshControl coloring is more likely to “take”

Sometimes the theming would be applied before the refreshControl was instantiated
Save/restore text color when inserting an image
Revert "Moved theming to viewWillAppear so refreshControl coloring is more likely to “take”"

This reverts commit 939b94ac61e803fa2f54b5d92b53884b7373e8e1.
Some CSS changes for dark theme and a new WIP settings icon. Settings
icon still being tweaked.