editor: fix Undo for Alter and Turn menus

Looks like someone figured out the problem, implemented the required
functionality... and then just didn't use it.
editor: fix crash on revert from disk

This still doesn't read in the timing data from disk, but hey, at least it
doesn't crash now.
default theme: fix saving of ThemePrefs

Since this was in a `decorations' layer, the outer ActorFrame was being
stripped along with its OnCommand.
JACK: fix race condition with decode thread

It was possible for the JACK callback to execute before the decode thread had
been started, causing an assertion.