Refactor send pane

Allows the user to send from any currency balance they hold so long as there is a path from that currency to the select currency to send.

Refactor:
- complete re-write of send controller
- Breaks send pane into 3 different templates (send form, confirm, result)
- Adds SendController as a parent scope for all three
- Adds SendFormController as the controller for send form

!$scope.send.destination.requireDestinationTag || !!$scope.send.destination.destinationTag