paginating project list

this fixes #189

Some thoughts: 

- I'm not sure about the page size. I set it to 20 because I believe that's enough, but it can be discussed.
- the project index.haml became a little ugly. I didn't find a way to make it pretty without messing things up (the "more" button always came to top).
- I also translate the i18n more button added via JS in the users index

Thanks