Renamed ScriptRange to FullRange.

User feedback found this more intuitive.
Adding PlaybackRange to the framesMode menu.

Now that we have menu items which don't map directly to enum values, we need to manage the selection menu ourselves.

Fixes #1007.
Forcing the framesMode widget to update.

This gets us the correct enabled state on the frameRange plug when opening the UI for the first time, and when switching between dispatchers.