Feature - Paulus 2 exception compatibility

This PR improves the Paulus exception handling and is a necessity for the exception changes in Rican7/Paulus#5

Other than the obvious constant additions for compatibility, this PR also changes how the base `Api` controller class handles exceptions in the `handleException()` method. Previously this method was passing the exception to the parent handler, but was never halting afterwards. This caused a condition that allowed the exception to be handled multiple times (once in the `if` block and once in the last default expression). This was causing a number of problems, including throwing eventual fatal errors and Paulus attempting to send a response more than once (oops!).