webadmin: Improved Comparable implementation of NetworkItemModel

NetworkItemModel now uses LexoNumericComparator in its Comparable
implementation, thus handling strings with numeric subsequences
better. This fixes the sorting of networks by name when they're
presented as contained in a NIC inside the Setup Host Networks popup
window.

Change-Id: I61e70d34f5dcd30ed85e898cd3bb0c47a6f4f7a9
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=915205
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=883269
Signed-off-by: Lior Vernia <lvernia@redhat.com>
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>