Making sure the "add files" button is always present, also when files
were already uploaded to an existing spot.
Communicator needs to append a port to the backendURL also if the
request is to be sent inside the local network, not only when it's on
your own development device. For example to check the page on the phone.

Of course this addition of the port to the backendURL can be omitted
when configuring a host on your machine and thus enabling the site to
be available at an address without an explicit port, but a lot of people
simply won't do this.
Setting an attachments property directly on the Spot model to hold the
attachments. This way we don't have to filter out the attachments
anytime we're submitting the model to the server. Furthermore we
override parse on that model because the server will respond with a
root key matching the class name as per the JSON-API spec.