Fixed #93. Send login once invite is accepted to get last_login date.

This fix might seem a waste for making a round trip. Well, the backend's
update_invite is monster and should be refactored to individual functions
to update both invite and user document. That being said, it isn't that
bad to make an extra round trip. It is a quick fix and actually does
reuse what has been implemented (login function in the frontend views
module).
Fixed #109. Dashboard has a <select> to choose which group to view.

First, this commit requires https://github.com/mozilla/minion-backend/issues/215
to be fixed and commits to be pulled in.

This commit has several important changes:

**HomeController is rewritten**
I have a problem with the original code. I need to save the promise
to be able to kill in-progress $timeout. Once I factored out I also
experienced multiple requests were fired concurrently. I believe
this issue would have been fixed by applying the fix below, but
since I already rewrote I am not going to bother verify my theory.

**Remove controller from $routeProvider's when(..)**
In ``minion-main.js`` we specify some routes and for each when(..)
case we specify the controller. I started out with a new controller
called ``Ctrl`` and then once the new controller was completed,
I changed it back to ``HomeController``. I then noticed two
requests were made. My theory was the controller was called twice
and I was right. I reduced to a single index.html and a single
controller. A quick googling yield https://groups.google.com/forum/#!topic/angular/pXQrhrL84Xc
.

The fix is to remove controller from the when().

**Add a "Loading data.... cloak**
When we move away from one group to another there is a 2.5 second of wait time,
I introduced a simple "Loading data" visual (demo: just look at how
http://plnkr.co/ did it).

**Allow group selection in the dashboard view**
This is the original task of this ticket.

**Thoughts**
This ticket took me a long time. A total of two days of efforts to find all kinds of
problems in how we use angularJS. I am hoping in the upcoming weeks I can
improve my angularJS skill.
Merge pull request #111 from yeukhon/issue#109

Fixed #109. Dashboard has a <select> to choose which group to view.