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 must be at least 8 characters" 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