Improvements to Angular support and user signup

Added "angular-comet" binding point in default.html, to allow angular
comet view stuff to go after other scripts, allowing for example
renderHeader in AjaxView to do things like setting up ajax GUIDs for
angular.
Documented AjaxAngularActionView.
Use a span in AjaxDataViews rather than a div.
Added action view to UserSignup to receive submitted user details from
browser.
Added show-errors directive and css for better form handling - now used
on user signup form.
Added password strength check and match check.
Added submit function to signup.js, this validates data and if correct
sends it to lift ajax handler - currently this is just logged on
server, will soon actually create a user.
Better form display on user_signup.html