Bugfix/rest api custom errors
This merge request reproduces some behaviour that got lost when we merged the three IRIDA projects into one and upgraded Spring Security OAuth2: the error messages produced when a client is not authenticated with the REST API are useless by default, so provide custom error messages to at least indicate what the client needs to do to authenticate with the server.
This involves some awful hacking around with internal OAuth2 classes because the authors didn't think that people would want to do anything other than their default behaviour.
I also took the time to clean up the class that's responsible for generating the custom error messages.
You can confirm that this works by using
curl on the command line to access anything served by the REST API without supplying a