Pull developer_name from manifest and use it everywhere (bug 785125)

https://bugzilla.mozilla.org/show_bug.cgi?id=785125

Fireplace part coming next, let's finish the review for the zamboni part first. This touches a lot of files, so I might have missed a couple spots... hopefully not :)

Will squash all the commits later, they are roughly grouped per page/functionality on the site.