[ContentBundle,WebBundle] Improve ContentBundle to use the power of
Symfony-CMF

Added possibility to add from backend :
- menus, 
- slideshow (with liipImagine filter), 
- routes to static content,

Added 3 slideshow location in layout. Display slideshow in top, content
and sidebar positions with sonata_block_render.

Menus could be displayed in frontend by simply calling knp_menu_render
and menu name (eg: {{ knp_menu_render('main') }})

Fixed some typos from previous ContentBundle commit, and create all
translations strings

Reorganize route and template by grouping them in a content dir for
better future maintenance
[ContentBundle,WebBundle] Fix some standard coding for PR 1962
Fixes to imagine block