Add calendar feed to dashboard for events and workshops

[jabelone]

Is your feature request related to a problem? Please describe.
Sometimes members might come on site to work on projects, but find there's a workshop or event going on. Most people are happy to work with the event happening, but some would prefer to organise a time when it's a bit quieter.

Describe the solution you'd like
A new integration that displays a list of upcoming events and accepts an ical calendar feed would be really useful to show to members. This way they can check the member portal to see a list of upcoming events in case they want to schedule a time around them (or join them!).

Notes
Now that celery is setup and working well, we can implement a scheduled task that continually checks and keeps events up to date for this feature to work.

[jabelone]

I am going to do this in three stages as explained below.

1. Develop db models and UI to support a list of upcoming events that have already been added to the database.
2. Create an iCal feed ingestion process.
3. Create a scheduled celery task to periodically scrape the iCal feed(s).

I have already started work on 1. and have been researching how iCal feeds work etc. in order to make sure stage 2 will work. I've finished most of the db models etc and will start on the front-end UI soon.