EZP-22654: Section create and edit

Link: https://jira.ez.no/browse/EZP-22654

## Description
Adds section create and edit.
It also fixes a few small issue  and CS.
I refactored two things:
- The way section list were returned (it now returns an array of objects instead of an array of array)
- I created a dedicated action to forward to when access is denied to a user (in PjaxController).

## Tests
Manual tests

## TODO
- [x] Apply PjaxController accessDenied to other controller than section.

## Screenshot (note that the CSS is not part of this PR)
![edit_section](https://cloud.githubusercontent.com/assets/4035241/4676438/0dc9ca6a-55db-11e4-8a50-59c9b9e14f8d.png)


Did we standardize this at some point?