added location to event and user to topic json

I am currently adding an auto importer to hacken.in to automatically import the events from onruby.de . For this I needed two more fields in the JSON result:

* the location of the event, there was only the id before
* the username for the user of an accepted topic

This is the "short route" to the result I needed. Another possible solution would be to add the json output to the location and user controllers. The downside with that would be that I have to trigger the api with more requests to get all the data. But if you prefer that way, I will throw away this pull request and create another with that solution.

I haven't updated the test because the tests just check if it renders json. I can update those as well to test against all known fields that should be in that json result.