Occurrences Model and API Fixes

[Vanethos]

• Removed null values from the occurrences API call query parameters
• Added a method to fetch single occurrence given the selfLink
• Added necessary attributes to the OccurrenceModel to have the prociv means of combat
• Added functionality to fetch single occurrence given the link to the HomeBloc
• Added click to fetch data and print it to the console on the occurrences list items