Make it possible to collapse refactoring changes in the diff window

[onewhl]

• See DiffWindow and DiffRequestGenerator classes to understand how the plugin generates diffs for refactoring changes;
• Differentiate refactoring and non-refactoring changes in files (check ranges);
• Close existing TODOs in refactoring-folding branch;
• Add information about the moved method to destination class as well;
• Check if a moved method was changed and add "moved with changes / with no changes" text to the description.

First, we should try to do it for one simple refactoring, for example, Move Method refactoring. Then, we will do it for complex refactorings that involve several files (like Extract Interface).

[e2e4b6b7]

Done:
Folding Move/Pull Up/Push Down Method/Class refactorings in main diff
Add hint in main diff where Move/Pull Up/Push Down Method/Class/Field refactorings detected

[onewhl]

Implemented in #81