webadmin: Add MAC pools in DC dialog

Added tabs to the add/edit DC dialog, old view is in a general tab and
a new tab for MAC pools. From this new tab, a MAC pool may be
associated to the DC by choosing it in a list box.

Change-Id: I338a5647ded866c6b7b07542e9a95ea3dc3a2594
Signed-off-by: Lior Vernia <lvernia@redhat.com>