Implements registrations and since last login information 

for global dashboard

- registrations over time chart
![alt text](http://s1.directupload.net/images/140531/7hhe3ynb.png "Registrations over time")
- dashboard boxes
![alt text](http://s1.directupload.net/images/140531/4rca83fd.png "Dashboard boxes")
Shouldn't that be start_date.year so that we get the year of the start_date ?!
My testing crashes at that point ( http://paste.opensuse.org/51194690 ), travis seems to be OK, dunno why...