Refactor the Nuxeo Server Section

Following our meeting around the new architecture of the Nuxeo Server section, we will now need your help on making sure that the existing content is up to date, add the content missing, etc. 

I'm moved the pages around as decided during our meeting in a branch: https://github.com/nuxeo/doc.nuxeo.com-content/tree/NXDOC-1765

Here are some notes on particular points to take care of: 

Repository concepts:

• Make sure content is up to date and concise
• Add content about rendition

Create a page "Configuring the repository"?:

• Put theoritical doc on Repository Concept
• Add link on how to configure schéma, doc type, lifecycle from studio doc 
• Blob provider: add link to file Storage

The JSF UI Framework entry will be moved under the JSF UI addon page by Doc team.