Improve Exception/Error handling logic, heirarchy, etc

[MikeNeilson]

          There is no parent class that RateException can extend?  Otherwise what keeps ApiServlet from filling up with implementation specific exception types?  I would think that if we really can't think of anything more generic at the very least we should be able to make a class for Controller exceptions and another for DaoExceptions depending on where the issue is.  I don't see ApiServlet knowing how to handle RateException in any helpful or meaningfully different way than other exceptions.

Originally posted by @rma-rripken in #1082 (comment)

Based on the PR discussion, we need to revisit the error handling. I think we have the crux of the right solution and some recent experience may provide us the next improvement.