Secure read/write of location storage on client

[luxx]

Requirements

• add secure storage of location to the client
• queries:
  -- select most recent locations, ordered by
  time
  -- delete locations after time X
  -- append new locations (time ordered)
• data should be encrypted at rest
• add the database contents (all data) to the src/components/DebugMenu so we can see how it works

Evaluate DB to use, Realm or SecureStorage + AsyncStorage.