Refactored action views, added transact

Moved some commonly used polymer client javascript stuff to Polymer
object.
PolymerActionView.scala now also has "transact" views, that allow
client to call a function with a guid, and get back the response from
the server into a closure, for round-trip data. For example, submit a
candidate user, and get back a string indicating success (empty) or an
error.
Polymer user signup now uses transact to give a nice friendly toast
showing any server error.
Renamed some client side functions - we now have a general "server"
function on elements and PolymerBoxes, which handles all data from the
server.