Add support for selecting ML2 Mechanisms

Along with exposing the options to select an ML2 mechanism, also add the
Cisco Nexus mechanism.

* Refactor remove element click into a function
Fixes bz#1141902 - Uncheck configured networks on Assign page

Remove row highlight
Merge pull request #328 from knowncitizen/bz1141902

Fixes bz#1141902 - Uncheck configured networks on Assign page
NIC configuration - Show 'Hosts to be configured' table
Merge pull request #323 from jtomasek/hosts_to_be_configured

NIC configuration - Show 'Hosts to be configured' table
Simplify ml2 mechanism "at least one" validation
Merge pull request #325 from bcrochet/cisco_nexus

Add support for selecting ML2 Mechanisms
Version 0.4.0
BZ# 1128282 - Remove descendant hostgroups from the foreman host form

Users should not assign hosts directly to the deployment hostgroups.
This removes those choices from the host edit form.
Extend the foreman API to disallow setting the hostgroup via the API