Add meta description to pages where it is easy

Lots of the page types have obvious content that can be used as a meta
description. In those situations we should use it. We will have to think
harder about what to use in other situations.

Added a helper to make adding a meta description easy on any page.

There probably should be a test for this to check that the right content is inserted. However, I am not sure how that should be implemented as we are trying to depreciate the use of view_test. Any opinons on how to add tests appreciated or if there should be tests.