Refactored action methods to their own file

There will be dozens of action and they have similarities in their
clean-up and undo behavior. Many actions will have influence to several
places: UI, forest, nodes etc. so they don’t have natural place where
they belong. Better have them as ActionMethods instead of distributing
all around the place.
Moved management of syntactical objects to ForestSyntax.

Lots of cleaning and debugging support.