* Interface is now selectable when multiple interfaces are available.

* Interface can be input in the Runtime Environment.

* v4 prefix is disabled when Enable IPv4 is unticked.

* v6 use is toggled by Enable IPv6 tick box.

* Add setSubnetCIDR, to programmatically change the value.

* Add signal for when the value changes.

* Ensure the proper amount of .0 octets are appended when the spinbox changes.

* Also ensures that the unused function in util/net (is_url_valid)
  doesn't break the build of network.cc (and vis versa for user.cc).

If a user account is otherwise empty, 'Admin' determines validity.

This is necessary in case someone needs font sizes raised.
Otherwise, content may be truncated.

If we pop a modal box before disabling the notifier, we'll get multiple
messages.  When a user clicks OK on the second message, it will attempt
to double-free, causing a segfault.  Whoops.

We restart wpactrl every time we do a new scan (for some reason?),
so we need to add the filters when we attempt to join or else they
won't be there.