AegisubLocale is created extremely early in the application
initialization, and using StandardPaths in its constructor resulted in
?user being set to an incorrect value as the app name hadn't been set
yet.

Use wxTranslations directly rather than going through wxLocale. This
significantly simplifies the code, eliminates the hardcoded list of
languages for non-windows, and makes it possible to use mismatched
languages and locales.

Closes #1508.

There's really no reason to present the user with a giant list of
checkboxes that lets them unselect at most a few megabytes of local
files.

When auto scrolling is enabled, scroll the audio display after a click
near an edge to mimic the effect of scrolling to show the new audio
selection (as 2.1.9 did), but hopefully without all the weird
undesirable cases that had.

It never allocated any non-autoreleased objects so ARC wasn't actually
doing anything other than breaking compilation with gcc.