When loading a settings pane, "loading" should be set to true to stop
signals being emitted by settings changes to trigger while the settings
are loading. This should have always been set here as well, but wasn't
detected so far because currently there are no settings in accessibility
that have signals connected that track changes.
Macros can be hard to read and are usually not very friendly to use in a
debugger. Using a static function instead gives the advantage of better
syntax highlighting in IDEs and better debugger support.
This change introduces an accessibility menu to settings, along with
options for overriding the colors used by OBS in the mixer and in the
preview to be more color blind friendly than the options provided by the
current theme.
