Cleanup.
Backoffice migration to Twitter Bootstrap 3 (login form).
- Added `MainMenu.addAsideTpl()` and `MainMenu.addAside()` to add aside boxes (aka "aside") in the left column.
- Added i18n aside as a template.
- Added SEO aside.
Merge pull request #528 from fredericbonjour/Admin

Added "Aside" feature in the left column and added Aside for SEO.