Detect duplicate macros (#1891)

[beckjake]

Fixes #1891

Originally I wrote this as a warn_or_error, but upon reflection that made no sense, as your code will almost certainly end up doing things you don't want it to do.

I added a little helper in dbt.ui.printer that uses the stdlib textwrap and dbt's PRINTER_WIDTH to generate reasonable-seeming output.

[drewbanin]

Jotted down some different copy for the error, but this otherwise looks really great.

I didn't realize textwrap was in the standard lib - really excited to leverage it more for things like this in the future! Ship this after those copy changes are addressed :)

[drewbanin]

can we format this more like exceptions.raise_ambiguous_catalog_match?

dbt found two macros named "{macro.name}" in the project "{macro.package_name}".
To fix this error, rename or remove one of the following macros:
 - {macro.original_file_path}
 - {other_path}