Handle serverside errors in Falcor better

[emilgoldsmith]

Expected Behavior

Serverside errors encountered in Falcor should be communicated better to the front-end. The front-end should be able to for example know what went wrong if relevant and maybe tell the user it was their mistake, or whether it's a bug

Current Behavior

Right now for example if the cache is corrupted so the front-end can't validate if an issue already exists correctly, it'll (even if strengthening our promise "catches" which they currently aren't) simply say it was a 500 error when it was a user error.

Possible Solution

Steps to Reproduce (for bugs)

1. Throw an error in Falcor
2. See ambiguous 500 error be transmitted, not the actual error