Bug fixed with localization of range edit window

Localization of Extensible.form.recurrence.RangeEditWindow did not work because it was a singleton and localization strings were applied too late (after an instance was created).
Turned RangeEditWindow into an non-singleton and use now Ext.WindowMgr to keep track of the only instance create of RangeEditWindow.

See also http://www.sencha.com/forum/showthread.php?128646-Singleton-vs-class-with-all-static-members about when instances are created for singletons.