add support for team devices

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
editor: use unambiguous mnemonic kyes for Team and TeamPort pages
libnm-gtk: recognize Team as a valid virtual device
team: make algorithm for choosing new team_num deterministic

The previous algorithm for choosing the team_num is not deterministic.

It does neither choose one of
(a) MAX(existing team_nums) + 1
(b) MIN(unused team_nums)

What it actually chooses depends on the order how the existing
connections are returned. For example:
[0 2] => 1
[2 0] => 3

Change it to use (a).

Signed-off-by: Thomas Haller <thaller@redhat.com>
editor: change JSON Team/TeamPort config widget from GEntry to GTextView

and allow importing the config from a file.

libteam configuration is a string that can be quite long, and simple GEntry is
not much appropriate for it. This commit uses GTextView instead, so that
structured multiline JSON config can be typed. In addition to that, the import
button allows selecting a file whose content will be imported as the config
text.
editor: only allow adding compatible slaves to master Team connection

Compatible slaves:
 - InfiniBand
 - ethernet, Wi-Fi, VLAN
team: merge a branch adding support for Team to applet/editor (bgo #708245)

https://bugzilla.gnome.org/show_bug.cgi?id=708245