Added SimpleResponder template. Can use this for simple responses, with a !ping example in the applicationContext.

Changed the !price command to use the sell average instead of all average.

Fixed a problem when !system wasn't provided with any arguments.

Fixed the code around finding current users when an api is being added to a new user.

Added initial Poller abstract class.

Put some exception handling around the responders to catch 403 errors. This should be made more specific!