Refactor Exception Handling

[mbabker]

• Change exceptions to custom exception subclasses for the component
  • Probably need to set up an autoloaded path for the component so the code isn't getting littered full of JLoader::register() calls
• Change controller to catch these exceptions (actually, just catch everything thrown when executing the component and keep it simple) and convert to a JSON response, not relying on Joomla's error handling layer because of the global exception handler being a rigid HTML format until 4.0