filter: Implement several small things after discussion

  * Add trashcan icon for newly-added actions
  * Categorize filter actions
  * Use imperative phrases for action descriptions
  * Drop check boxes from simple actions (like reject ticket)
  * Hide empty forms on new ticket pages
  * Do not store config for nondata fields for actions
  * Implement a multi-use feature for actions, which will allow using a
    action more than once (for instance, multiple email sends)
  * Filter actions are sortable
  * Send email has from address configurable
  * %{user} token is valid as a recipient