Refactor interface between CEKeyBindingManager and CEApplication
Add "changeTheme:" to ignoring list for keybindings
Extract CEKeybindingsSheetController from CEKeybindingManager (ref #53)
Use the same outlets in key binding sheet controller
Move sendEvent: method to NSWindow subclass

Since `sendEvent:` method which was overrided in the CEApplication class was actually needed only while inputing shortcut key in the key binding editor sheet, I've moved it to the new made NSWindow subclass and remove the CEApplication class.
Make some methods in CEKeyBindingManager class method
Clean CEKeyBindingSheetController class
Merge branch 'refactor/keybindings' into develop