Update vimeo library

Few points to note with this PR...

1. All the feedback received on the last PR has been addressed (anything in the commits prior to 26th August) so hopefully only the stuff after the 26th needs to be reviewed.

2. The new Vimeo API uses oAuth, rather than create the entire oAuth dance I've added an oAuth Access Token parameter to the config. This shouldn't expire but obviously not ideal long term. 

3. The values from the Vimeo API response were getting output directly in the template before, the new API returns a completely different structure to the old one which meant changing the templates. To avoid this happening again in the future I've abstracted the logic from the view and created some Video classes to parse the data so should be much easier to handle changes going forward.

4. The dukt vimeo library no longer supports caching, this could be done in Silex but would impact on pagination (e.g. videos might 'go missing' if some pages are cached but others aren't) - not sure how best to approach that? Advice massively appreciated!

Please be nice and apologies for the delay on getting this up... :)

Cheers,
M

Happy to switch to a library. Who do I ask to get more time to spend on this?!