Better behavior when no configuration file is found

Follow-up on #497.

Using a configuration file is optional. As such, the configuration defaults to an empty object when no configuration file is found. No exceptions are thrown.

Please note:

• when no configuration file is found, we do print some message indicating no configuration file was found.
• when a --config path was explicitly specified, we do throw an error if it cannot be found

However it might be possible that no configuration files might have been found due to wrong user configuration. The only way I can think of would be when the configuration file was saved under a wrong filename. We could use Levenshtein distance or similar approach to try to guess when this happens, in order to print an error message.

[jlengstorf]

Personally, I wouldn’t close this until there are links to docs in the warnings and/or an issue is open to create clearer docs around defaults and config composition.

[DavidWells]

For example setting any config in the dev section causes dev to break without all options being set (as far as I can tell; lots of port errors).

This sounds like a dev error in the CLI. There is a-lot of confusion around the netlify dev settings and ports in general https://github.com/netlify/cli/issues/563. If you have ideas to make netlify dev and it’s related configuration please let me know 😃