Remove data-field in arkadevent

[cNille]

A data-field was added to the arkadevent-model. This is used when in list is fetched in the server and the "isRegistered" is to be added to each event object.

isRegistered is a value to show if the user that made the request already has registered to the specific event. But because isRegistered isnt in the arkadevent-modell it isnt sent back to the client. Therefore i've put it in the the data-object which is defined in the modell. This is a ugly hack to work around the problem. Try to find a solution where a data-field isnt needed!