Portal 2

This pull requests introduces major changes to bennu-portal.

It is now able to properly deal with Semantic URLs, multiple presentation technologies (i.e. backends), and it provides server-side layout injection (previously it only provided client-side).

Also, templates are now written in Twig, and the rendering engine is automatically loaded.

Lastly, `bennu-admin` has been rewritten, it is now built using Angular.js, supports the new Bennu Portal and provides several new features:
  - System Information panel with JVM statistics
  - Dynamic thread dumps
  - Domain Browser, allowing online inspection of the domain