Query optimization assistant Joe now supports Web UI and multiple databases

Joe, a chatops bot that uses fast thin clones of full-size databases, is
upgraded to the 0.7.0 version: https://postgres.ai/blog/joe-0.7/.

The new version makes it possible to expand the available types of
communication and implement support for any messenger. Joe Bot can be now
integrated with Postgres.ai Platform providing Web UI to troubleshoot and
optimize queries. Web UI also brings one-on-one communication and
visualization options.

Two new commands were added:
- "activity" to monitor currently running sessions
- "terminate" to terminate long-lasting queries

Links:
- The blog post about Joe 0.7.0: https://postgres.ai/blog/joe-0.7/
- Joe command list: https://postgres.ai/docs/joe-bot/usage
- Joe Bot Tutorial: https://postgres.ai/docs/joe-bot/tutorial
- Community Slack (English):
https://database-lab-team-slack-invite.herokuapp.com/. After joining, the
live demo is available in the #joe-bot-demo channel:
https://database-lab-team.slack.com/archives/CTL5BB30R
- Git repository and issue tracker: https://gitlab.com/postgres-ai/joe
- Docker images: https://hub.docker.com/r/postgresai/joe