Raise exceptions (and catch and return them) instead of returning them directly as a string

[chuck-sys]

Please give a one-sentence summary of the cleanup you would like done.
Raise exceptions and catch them outside of the handle helpers in commands.

Please give as many details as possible about the cleanup or refactoring.
We will need to raise exceptions instead of returning a string. This will be a medium-sized cleanup that shouldn't involve the tests if we do this right (by positioning the error handlers in the right place).

Please list any additional context; in particular, list what areas of the code base this would affect.
I don't think that helper functions need to handle/know about how to output errors and should just propagate it forwards.