[TR #89] Modify list function to support paging

Allows the list function to be passed start/end options, which allow paging the list of errors (errors are now sorted by error id in order to insure consistency.

Additionally, a min-occurrences option was added, which specifies the minimum number of occurrences required for an exception to be returned. This is used in the front-end and set to 1, in order to only display the top-level exception for exception chains.

Tests were added for both the list-errors and handler function.