Refactoring changes

[lacedwithennui]

Changes:

Changes to the Codebase:

• New Response class which contains an HTTP code, headers, and a body and is built with a fluent interface design pattern and can be converted to spark.Response objects
• All Mongo.java helper methods now return Response objects
• Somewhat better error handling
  • All server errors caught in try/catch blocks return as error code 500 (except where there is a more descriptive error code, like when a resource is not found on the database)

Changes to the API:

• All errors now have a consistent response pattern of {"error": "[error message]"}
• All errors have relatively descriptive error codes
• All responses are now valid JSON
• New simple /endpoints API endpoint which returns endpoints and their valid methods
• Remove redundant /db URI prefix from all endpoints
• Listen on port 5002 instead of 5003 (for nginx proxy)