Update instructions for developers.

- Some of them were get from bitmask_client docs.

This closes #4185.
Update databases list, add tapicero to misc
Create tapicero.md

Copy tapiceros readme into leap_doc.
Add tapicero to menu
Add database setup section to overview

Explaining setup of 'normal' and per-user databases. link to tapicero, point out where the design docs come from and where they go.