Move sandbox error messages next to the input area with the bad input

[popematt]

(Suggestion) I think like green(success) and red(danger) should be the colors for valid and invalid validation results respectively.
And yellow(warning) should be used when there is an error in loading the schema or getting the type definition.

Yeah, that's what I had initially, but I thought that invalid inputs to the sandbox (an error) deserved the more "severe" color than data not matching the schema (a non-error).
If I was better with web development, I would prefer to have an error message next to the input area with the bad input, and then we wouldn't have to worry about having the same color for "does not match" and for "user error".

Originally posted by @popematt in #83 (comment)