* Add support for contacts with more than one Signal account using ContactAccount class.
* Use OWSTableViewController in contact-related views.
* Let users add non-contacts to groups.
* Improve the "new group" and "edit group" views.
* Add utility methods for displaying alerts.
* Warn users before discarding unsaved changes in "edit group" view.
* Pull out "contact view helper" to de-duplicate common logic among contact-related views.
* Pull out "group view helper" to de-duplicate common logic among group-related views.
* Pull out new base class for view used to add accounts to groups or the block list.
// FREEBIE
* Improve handling of accessory views/types.
* Use contact cell in “new/edit group” view.
* Don’t hide blocked contacts and group members in “new/edit group” view.
* Let users “unblock-to-add” blocked contacts in “new/edit group” view.
// FREEBIE
