Govmapper

will close #116

## Todo
- [x] "Site preferences" article
- [x] "Using Screendoor with GovMapper" article (requiring admin confirmation, etc.)
- [x] "Viewing your map" article (public-facing UI)
1. this link is broken when viewing from http://knowledge-base.ka/articles/govmapper (disregard my hostname)
2. why are our tests not catching this?
3. i'd rather not use this "to get started, click" pattern on these index pages. We already have the funky hand icon.