Fix/warn unknown formats

[epicfaace]

Reasons for making this change

Fixes #961. Allows for unknown formats to still work as per the JSON schema spec. Does the following:

• console warn on unknown format errors instead of showing an error
• default to default widget if the string format is not found (otherwise, providing an unknown format will look for a widget for that format, then fail)

If this is related to existing tickets, include links to them as well.

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests
  • I've updated docs if needed
  • I've run npm run cs-format on my branch to conform my code to prettier coding style
• I'm adding a new feature
  • I've updated the playground with an example use of the feature