use momentjs for nicer dates

Work in progress, replace datetime with nicer date 

As my brain-iso-date-parser is slow, I prefer to have computer do the work. I tend to better understand things like :
    - a few seconds ago
    - a minute ago
    - 5 hours ago
    - Yesterday at 5:67 PM

... etc

see http://momentjs.com/docs/#/displaying/fromnow/ and http://momentjs.com/docs/#/displaying/calendar-time/

Hover on date show long localised version (`LLLL`): 

`Month name, day of month, day of week, year, time`, e.g.  	`Thursday, September 4 1986 8:30 PM`

Of course the dom is updated regularly to reflect the fact that time passes.
![capture decran 2014-07-24 a 22 39 38](https://cloud.githubusercontent.com/assets/335567/3694468/af327858-1372-11e4-8f0d-70e250b7d720.png)

Yes I know I live in the future for you :-)

Ok, I will re-add `display:none`... (we can still make infinitely long title). What about also changing the "Last Checkpoint" text to an icon or something shorter.