Remove from DB on Task Exit

[yeslayla]

Currently, data is only removed from DynamoDB on POST /stop_server this should be changed so that data is instead removed from the database when a task stops.

This can be done by using CloudWatch to call a lambda script of a task stopped event.

[yeslayla]

Tasks left to do:

• [ ] Get the following code to retrieve the task's name

      # Lookup item in table
      aws_resp = table.query(
          IndexName="name",
          KeyConditionExpression="task = :a",
          ExpressionAttributeValues= {
              ":a": task_arn
          }
      )

• [ ] Update IAM permissions for CloudWatch Event