webadmin: Implement sorting for RxTxRateColumn

Implemented default client-side sorting for RxTxRateColumn, and
switched it on for the Network/Hosts and Network/VMs subtab columns.

Change-Id: Ia0a9b91350e774639a7879e26456f6e8cc15ba3d
Bug-Url: https://bugzilla.redhat.com/1120054
Signed-off-by: Lior Vernia <lvernia@redhat.com>