Different filters for board term entityreference fields depending on whether your an admin or a clerk user

Clerks only see their city's stuff. Admins see everything.

These commits include:

* Custom entityreference selection plugin that allows for selecting separate views for admin and non-admin users
* Update of Board Term Board and Member field to use the custom selection plugin
* Update ``my_boards`` view to include display used for admin filtering (just selects by Board type, doesn't do any other filtering)
* New view for filtering Members, ``my_members``

Note that all the behat tests now pass! :grinning: