Lotsa metrics + database cleanup + public dataset API

The theme of this release is: metrics.

On the server side, we have (#310):

• Metrics API that returns daily, monthly, yearly summaries of various metrics,
  both wrt local time filters and UTC timestamp ranges.
• New metrics screen that shows trip count, distance and duration over time,
  split by mode. On the server, these are aggregate metrics - on the phone,
  they are individual metrics.

Thanks to @yw374cornell, we now have a new public API for pulling data from the
test phones from the server. This is the first step towards creating a public
database that can be used for power/efficiency tradeoffs. (#312, #317)

We also have several other cleanup fixes.

• Unify, extend and fix bugs in the built-in timeseries implementation
• Refactor the query that excludes test phones
• Clean up analysis timeseries code
• Fix several bugs found by running automated tests after cleanup
• Fixed local_date semantics to better match timestamp semantics
• clean up the database queries to remove obsolete collections
  get_trip_new_db(), get_place_db(), get_section_new_db() and
  get_stop_db() and their references.
• refactor the index generation code and create a bunch of new indices for the
  analysis objects
• Reuse mongodb connection across multiple collection retrievals. This improves
  performance and prevents exhaustion of incoming connections.
• Move all logging config to the main function. Module level logging config is
  bad because it can override logging configs in other modules, depending on
  import order.