New Postgres backend and upgrade to Python 3.8

This release upgrades to Python 3.8 and removes reliance on ndb from Google. This now allows you to run on either appengine or AWS using a postgres instance.

2.0.1: Fix esling config (#113)

• Include the meeting title in the email. This disambiguates emails if a person is subscribed to multiple subscriptions.
• Rename .jsx --> .js and re-enable JS tests and linting

Fix #64, Subscription meeting creation bug

The fix for #64 requires a different way to store subscription times. In the past the user would put in the time in the given timezone. Now the time is given in UTC and the timezone is supplied as additional metadata.

For example:

I want a subscription to happen at 1PM. I fill in 1:00:00 PM UTC in the date field and America/Los_Angeles in the timezone field.

Modify Metrics Endpoint

Only affects users of the metrics api. This updated adds three new endpoints: /metrics/v1/subscribers, metrics/v1/meetings, metrics/v1/requests.

Patch error for unsupported number of users in group matching

Fixes an error that prevents all emails from being sent for other subscriptions if there are an unsupported number of group users in a subscription with group_size>2.

Group Matching Functionality

Group matching feature (#102)

* group matching

* simplify naming, add tests, add docstrings, enable group size in tasks

* fix linting errors