Changed: customization screen

Before merging, here are the main things to review:

* the right menu is buggy on mouse over (1px shift, chrome only): I haven't succeeded in fixing this
* I want to add a "?" button on the custom screen. On mouse hover, it will display information about the various layouts sizes and related devices), but we already use the "?" et and the "!" icon in the home for other purposes. Any ideas?