Refactoring testing code and testing ui cancel buttons

- Test for cancel button behavior on dialogs
- Added select-menu and transition to tests
- Added specific dialogs and rearrangeed how they're setup and linked with menus (the menu item doesn't instantiate anymore, and, instead, just takes a reference).
- Refactored for clarity and abstracted:
  - About dialog
  - Ok-Cancel dialog
- Some follow-ups from previous PR

@devoncarew @dinhviethoa 
This actually is a single instance (a singleton).  I was trying out using factories for getting an instance as detailed [here](http://stackoverflow.com/questions/12649573/how-do-you-build-a-singleton-in-dart).  Probably too confusing to use, so I switched back to traditional `.instance`.