improve error handling

[hhsnopek]

this is based on #82

• Improves error handling

Caveats

• Reshape errors display parsing errors, from reshape core, rather than the Error w/file:line:column. This pull request does not fix this issue, the fix will have to be completed in Reshape itself.
• Postcss/Babel errors are displayed as "WARNINGS" (no clue as to why)

Previews

NOTE: Project names were redacted.

Postcss Error

DatoCMS (app.js) Error