[WIP] [bug 969667] Merge desktop and mobile forms

This is a work in progress. It sort of works, but has a bunch of issues that I can't figure out. To access it, go to http://127.0.0.1/en-US/feedback/generic .

Problems:

1. On big screens, I find the text hard to read and cluttered. It's also all bunched up at the top in the middle. Media queries can probably help fix this, but my media query fu sux0rz.
2. The browser's back button goes back a page in history--it doesn't go back a card. That's not a big deal with a mobile browser where you can see the web page back button, but hugely problematic on desktop where it's really far away from the form and it's very likely someone will try to use their browser back button. I don't know how to fix this offhand, but I think I have to use push state (or whatever it's called).

Beyond that, I think the privacy messaging and the labeling is better. This includes the url field that the mobile form doesn't have currently (win!) and it's easier to read than the desktop form (win!).

Also, I'm creating new .css and .js files and duplicating some things right now. I'll fix some of the duplication (duplicate images, duplicating in .less and .css files between this new form and the Firefox OS form, etc) in a later refactoring pass.

Anyhow, work in progress.

Feedback?