Add time since the last update in the HTML view

Using Satis every day, we are often waiting for it to be built after a git post-receive. This little improvement reduces the energy that is needed to find if the last change we pushed has been included in our satis.

![satis](https://f.cloud.github.com/assets/400034/1722809/6ee0bcfc-624b-11e3-9df9-3ba60b015ed1.png)

The date of the last update is renderer with moment.js

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT