Modularize Aphront exception handling
Currently, all exception handling is in this big messy clump in AphrontDefaultApplicationConfiguration.
Split it out into modular classes. This will let a future change add new classes in the Phacility cluster which intercept particular exceptions we care about and replaces the default, generic responses with more useful, tailored responses.
- Hit a Conduit error (made a method throw).
- Hit an Ajax error (made comment preview throw).
- Hit a high security error (tried to edit TOTP).
- Hit a rate limiting error (added a bunch of email addresses).
- Hit a policy error (tried to look at something with no permission).
- Hit an arbitrary exception (made a randomc ontroller throw).
Reviewed By: chad
Differential Revision: https://secure.phabricator.com/D14049