Proof of concept

Need to be extracted into model and covered up with tests.
Create FileManager Model and its test case

Started to extract method from controller to this model.
Replace controller method with model one.
Create rename() method and cover it with tests
Make configurable editable and deletable paths.
Refactor rename action to use method from model
Add missing namespace for FileManagerAppController.
Display rename action in row actions area
Prevent overwriting existing file and redirect to referer
Docblock fixes and deprecate _isEditable() and _isDeletable()
Merge branch '2.2-filemanager-rename' into 2.2

* 2.2-filemanager-rename:
  Docblock fixes and deprecate _isEditable() and _isDeletable()
  Prevent overwriting existing file and redirect to referer
  Display rename action in row actions area
  Add missing namespace for FileManagerAppController.
  Refactor rename action to use method from model
  Make configurable editable and deletable paths.
  Create rename() method and cover it with tests
  Replace controller method with model one.
  Create FileManager Model and its test case
  Proof of concept

Closes #293, #559