Expand event helpers
Expand event helpers

Extends triggerEvent, allowing the creation of
different types of event, and to change the data
on its object. Also fakes the positional data
browsers add to the event object.

Also adds helpers for simulating:
- all the events for a mouse click
- the events invovled in moving the selection in a radio group

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin