Replace old action API used by refactorings with newer handler API

The names of refactoring classes that provide an integration into the UI
of Eclipse have changed, in order to minimiz overhead in the class
names.

The previous code contained some logic that should disable a menu item
when nothing is selected in the editor. But the existing logic was
wrong, it did never work. Because I did not find out how to implement it
correctly with Eclipse core-expressions I romved the logic completely.

Formerly, the context menu item, that showed the refactorings, contained
an item to the "refactoring qick menu", which has now been deleted. This
menu contains all available refactoring and it can be display by
entering a key combination. This item doesn't provide additional
information, thus the deletion. Users can always look up the key
combination in the preferences.

The ids of the commands have changed - thus, the preferences of users
are no longer considered for the new commands. To avoid this problem
the class `MigrationPreferenceInitializer` is introduced which can copy
old preference values that are defined by users and set them as default
values for the new preferences.

Fixes #1002049

Todo:
- look if change of id is useful
- merge EditorUtils and EditorHelpers
- implement context menu in plugin.xml