Move text pre-processing functions to Aegisub-Motion.moon

Functions that need to be tightly integrated with aegisub-motion
specific options have been moved to be purely internal.
Add a bunch of junk to Line.moon
Add guards to line transform (de)tokenizing.
Options is no longer an instance variable of a LineCollection.

It was dumb and bad.
Detokenize transforms in motion processing function.
Fix shadowing @ in gsub callbacks.
Reference tPlaceholder properly.
Misc fixes.
Keep interface updated between the clip and main windows.