webadmin: Enabled column resizing in Manage Cluster Networks

In certain locales columns would get wider, to the point where a
horizontal scroll bar appeared. This fixes it. Also adjusted some
preset widths to look better in English.

Change-Id: If7bac93b4de9400996a07ffc98fed3a6343fef34
Bug-Url: https://bugzilla.redhat.com/1009745
Signed-off-by: Lior Vernia <lvernia@redhat.com>