Mobile/Fennec/FormAssistant2.0

Form Assistant has been done just before RC1 of Fennec 1.0 and it looks a little odd into the actual UI. It needs a visual refresh as well as a better definitions of some behaviors.

Todo for visual refresh

- FormAssistant and Find In Page has in common the navigation between results of a page, and for that we want to use commonly the next/previous buttons and replace them by an arrow

- Remove the close button but ensure that closing the FormAssistant is easy and easily discoverable

- Implement the visual behavior from https://wiki.mozilla.org/Mobile/UI/Designs/TouchScreen/Fennec_1.1%2B/Revised_Functionality_and_Layout_of_Form_assistant

Todo for functionalities

- We miss a lot of tests for the uncommon functionalities of FormAssistant, like preferences and edge cases

- Decide how to handle the case where the content of a list item is dynamically generated

- I think we should listen focus change in some ways (at least when the assistant is opened) and react to update the assistant because some form fields do some crazy things duuring the focus (like changing the active field)