[WIP] partial port to bootstrap

Currently breaks everything (main page).
Partial port of header to bootstrap. Improvement of display on little screens.
Help required.
@svbergerem : I'm a bit worried about this part. I wonder if I should drop the old way of doing to replace it with the bootstrap's embedded dropdown menu or if I should minimize the usage of bootstrap.

Currently, the bootstrap integration breaks the presentation of the notifications dropdown.

![sync_opt1](https://cloud.githubusercontent.com/assets/3429231/5488291/f9b4900c-86bb-11e4-82de-cb80ef3bc813.png)

IMHO, adopt the full BS usage would reduce a lot the size of the template and stylesheets. But I'm concerned it could have some side effects.