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 
I meant that this:
```
    ).then((_) => menuItem.dialog.onTransitionComplete.first
    ).then((_) {
```
could probably be changed to this:
```
    ).then((_) => menuItem.dialog.onTransitionComplete.first
    .then((_) {
```