APF-404 subtask: signup.html improvements

signup.html:

ognl:components.foo --> component:foo

These binding prefixes ("component:", "asset:", "bean:", "listener:", etc.) are more than just improved syntax over "ognl:". The corresponding IBinding implementations use type safe, non reflective calls. The "ognl:"
prefix makes heavy use of reflection. Further, Tapestry is able to identify that the other binding prefixes are "invariant" (i.e., will always return the exact same value) and will cache those values inside component parameter properties aggressively.
Over the course of processing a client request, once both the application and HotSpot are warmed up, this might add up to a measurable amount of time.

Tapestry does generate JavaScript to focus on the first field in a form. The logic has improved in Tapestry 4: its the first field in error, or
the first required field, or just the first field.