Allow for query string configuration

This commit allows for the activity stream module test page to be
configured using query string parameters. Specifically, it allows the
test API endpoint, user type, and user ID to be set using `api=<API>`,
`type=<TYPE>`, and `id=<ID>` respectively. For example, I could visit
the activity stream module test page locally and configure it by
navigating to:

````
http://127.0.0.1:9000?api=http://my-activity-stream-server.com:80/&type=rap_cat&id=420
````

Please note that API endpoints must have a trailing slash.