Testing closing of several dialogs

Testing opening and closing of:
- git-clone action
- help-about action
- new-project action

Also:
- setup transition-complete event on spark-overlay and listen for it in tests
- refactor access classes into separate file.
- fix several nit issues (copyright and library names)
- checking visibility with `elementFromPoint` instead of `display` / `visiblility`

@devoncarew @ussuri 
Generally, I like to avoid strings for referring to items as there is no identifier checking (if there is a typo, it can be hard to find).  I make exceptions for places that absolutely need to be loosely coupled, but that shouldn't be the case here.  I actually change the structure of this in the next PR (building on this one) and it looks much better (passing dialogs to link to menu items instead of letting the menu item instantiate them).