Checkpoint for the frontend

Hey,
I have talked during the past few days with @bcipolli and we decided to merge my branch. It allows us to have a code review of the changes I've made. In the past, we used to merge changes on my branch and it was kind of a painful process. I think that merging with the develop branch and making small pull requests is the way to go. The development will go faster and allow other people to participate. Moreover, a lot of people want to make small HTML changes and having bootstrap will help them a LOT.

@jamalex Right now I've implemented Grunt.js for the compilation process. I think that implementing django-compressor should be another pull request.

What is the problem you're trying to solve?
- Have a better stack on the frontend
- More control on the css
- Cleaning up the central server files
- Allow people to create templates easily
- Make a better experience for new frontend devs

What is the design of your change?
- Integration of bootstrap in less in the assets folder
- Refactoring of the css in less
- Implementation of Grunt.js for the compilation
- In Debug mode, less.js will compile to css (the css files are cached in modern browsers). In the production mode, the template will use the css generated by Grunt.js

How did you test the change?
- `grunt` to compile to css
- I have reimplementated all the templates of the central server in less with bootstrap