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. Removed this sentence anyway.
2. The link-checker wasn't checking *any* of the new govmapper pages, presumably because there isn't a link to any of them on the home page. I added one to the home page and it checked them all, so this must be it. Kinda lolzy, but makes sense as the only way to get to any of these pages is via the dropdown. Now we know, so it shouldn't happen again. Could make a site map/index to avoid the possibility of this happening again, but it's probably not worth it (we'd normally link to a new app from the home page before pushing to production anyway).
3. Yeah forsure. However, the funky hand icon *is* kinda funky. Maybe we should re-think how we want to display these app index pages. I have some ideas, so I'll try to work on that (with #75) after GovMapper/Notifications are taken care of.