Tooltips are now done programatically.

* Prepare for IE8 which has no `content: attr(title)` CSS support.
* Position the tooltip programatically to avoid problems with password help text.
* Eliminates the extra HTML needed to position tooltips.
* Fixes the "password help text" now displaying when focusing the password field on /signup

fixes #492
fixes #498
fixes #525
Add unit tests around trackSubview and untrackSubview.
Hide tooltips on element 'change' event as well.
Merge pull request #526 from mozilla/tooltip-refresh

Tooltips are now done programatically.