Admin Panel enchancements

[nikhil-thakkar]

This relates to #16.

Changes requested:

1. Add a description text field for each talk session.
2. Add related tags for each talk session. For e.g.
   If the talk is related to some kotlin feature, then the tags can be mobile, android, kotlin, feature.
3. Ability to edit a previous/current event.
4. If possible use of service worker to do some background task. In this case creating an event in Meetup. More details here Creating a new meetup on meetup.com when a new event is pushed to the db and activated. #6.