Flask microservice + shared DB package

[jessiclassy]

new parallel service calendar-feed serves up Flask application to produce subscripton calendar feeds:

• Service endpoints:
  • /health should return {status: 'ok'}
  • /status should return last deploy time (nice-to-have for DigitalOean)
• .ics subscription feed endpoints
  • /feed/chamber/<chamber_id>
  • /feed/committee/<committee_id>
  • /feed/org/<org_token>
  • /feed/user/<user_token>
  • /feed/working-group/<user_token>
• JSON feed endpoints as an option for web app consumption or future API offering
  • /feed/chamber/<chamber_id>/json
  • /feed/committee/<committee_id>/json
  • /feed/org/<org_token>/json
  • /feed/user/<user_token>/json
  • /feed/working-group/<user_token>/json

Also included in this PR is a shared db package

• DB package contains functionality to share across feed, web app and other future services
  • db.connect returns a connection through a context manager, from db.connect import get_conn; with get_conn() as conn...
  • db.tokens defines relevant calendar access token functions
  • db.admin defines relevant admin-only functions for calendar access (backfilling tokens, clear/reset)
  • db.calendar_queries defines shared queries between web app calendar page and Flask calendar feed
• Service Docker container must be run from repo root (must alter DigitalOcean source directory to match)
• NB: DigitalOcean app spec needs to identify Dockerfile location within the service package