New nav post-launch checklist

[souperneon]

• [ ] Figure out Metro Extracts login stuff https://github.com/mapzen/metro-extracts/pull/283
• [ ] Keep dropdown open on mobile https://github.com/mapzen/metro-extracts/issues/284
• [x] Centralize where docs-generator & metro-extract get header from

[migurski]

Docs-gen and Extracts both get their headers and footers from a central location:

• https://github.com/mapzen/mapzen-docs-generator/blob/master/Makefile#L89-L93
• https://github.com/mapzen/metro-extracts/blob/master/App/util.py#L84-L88

[souperneon]

Moved here https://github.com/mapzen/website/issues/1259