Because if we have a latest pages block but no group pages listed then
the template will not initially compile as there has been no call to
require lib/group.php

Actually we should avoid having non basic function calls in the template
so I'll move all instances of group_homepage_url() in templates out
to the php that generates the data.

behatnotneeded

Change-Id: Ia804fee854418e7b3b3620c998f2219a0b0d6f25
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>