Changeset 491 for translations/da

Added plog_tr functions in the entire gallery (not just the admin), so that everything is now translatable. For themes, only the default theme is translatable.
Translated the entire gallery to danish.
Added code to allow videos, showing a thumb-nail for a video instead of returning an error.
Ajax editing of international characters in caption, now shows the correct characters.
Tested code that jumps down to id tags for previous and next buttons, code not active, I am not sure whether or not everyone want this behaviour.
Tested a new installation based on the code.