Tweak site indexing to include all pages

The current search indexing only looks at "regular pages". This ensures
that a lot of the content is indexed and avoids the indexing of taxonomies
and other broadly irrelevant types of content in the index. However, it
does result in certain lists pages not being included in the index that
may contain valuable information.

The value of having the list pages indexed currently outweights the impact
of potentially including other tertiary data in the index, for a start
we're not currently using taxonomies. This should be re-evaluated as and
when we're able to spend time better structuring the website.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>