Importing a config with the Custom JS widget breaks extension version

[the-wright-jamie]

On the web version of Tabliss and Tab Nine (Tab Nine web edition is currently not hosted anywhere), there is the ability to add a custom JavaScript widget. While this is a very powerful feature, the execution of arbitrary code is currently forbidden by most web stores - for good reason.

However, exporting a config from the web version and then attempting to use that config on the extension version will cause Tab Nine to be unable to load.

This is a serious issue, as it is then difficult to reset Tab Nine to a working state. While trivial for a user who knows their way around developer tools, a non-technical user will have no chance of fixing this themselves (although one could argue that no non-technical user would be writing Javascript, and thus if they get in this situation would know how to escape it).

Regardless, this is a bug that needs to be fixed in order to prevent this from happening again.

Possible Fixes

1. Remove the custom JS widget entirely
2. Add a check that runs during import of json that blocks custom JS (and present a warning)
3. Don't export the custom JS in the first place

[the-wright-jamie]

Fixed by creating a failstate where 'unknown widget' is used as a placeholder for expected widget