Introducing a new way to structure content and sections.

This pull request aims to use a new way to handle projects files with the ability of jekyll's collections. 
The projects are no longer kept into `_include` folder but they are transfer into a dedicated one named `_projects`. 

I've used [Jekyll collections](http://jekyllrb.com/docs/collections/) to obtain the ability to create a new type of data, in this case a project data. 

The assets file are in the same place.

There are also a change in the ability to select the order of displaying the sections of the site. 
This introduce a new way to handle the section for future users and also if we want to customize more the template we can create new blocks to add more personal style to our site. 

Last minor change is about the thumb images in the work sections that now are actually content of the page, inside a `<img>` tag and no longer inside a style tag.