CMFileManager: Make use of plurals correctly

* Make selection strings use of plurals allowing to translate these into
  languages where the logic of plurals is different than in English.

* Rename some plurals as these are not used only in properties dialog
  any more.

* Remove quantity="zero" cases from plurals as these are never used in
  English.

* Remove now unused strings from translations and rename plurals.

Change-Id: I8c07f1ba85b208d37626106e0e2f691468c1cbc4