basic topics page
Update link to volunteering page.

Fixes #133
Merge remote-tracking branch 'origin/493-topic-page'
Merge branch '505-external-links'
Switch to using Foundation v4.2.3 via a submodule

Previously we made the assumption that someone had installed the
zurb-foundation gem somewhere accessible, e.g. via
"sudo gem install zurb-foundation" or in an rvm gemset.  However,
there's no need for this assumption, since we can just point to the
version of Foundation that we require as git submodule.

This uses Foundation v4.2.3 which was the version being used
previously on our servers.
Install the compass gem locally for the deploy.bash script

Rather than relying on a (possibly outdated) version of the compass gem
being install on the system, just install the gem into a gems directory
at the same level as the repository root in deploy.bash.  It's only used
by the "compass compile" command later in that script.
info panel style for bottom of MP page
equal heights for info panels