Add titles to most pages

[gravitystorm]

There's a lot of pages that are missing useful titles in the html headers, such as the about, help, communities, fixthemap, welcome pages. We should add the set_title helper to each of these.

It might be possible to detect the use (or lack thereof) of the set_title helper, so that when we add pages in future we know that an appropriate title has been set. Either using a home-grown linter, or by using something like the cancancan check_authorization