Translate two strings which were previously untranslatable in mythmusic.
Reduce flashing of images when moving through a buttonlist.

Refs #11717
Don't clear a MythUIImage widget if the new image is coming from the
cache, makes for a smoother transition.

Refs #11717
Don't display the new button state until we've finished populating it
with the new values. Fixes another visual irritation.

Refs #11717
Don't force background loading for remote images if they are already
in the memory cache

Refs #11717
Increase the lastmodified check interval from 5 to 20 seconds on cached images. Refs #11717
Increase the Max image cache size from 20MB to 30MB. Refs #11717