Can't import configuration file with outdated plugins in it

## Describe the bug
If you try to import a configuration file which has a plugin in it that isn't present in the data directory, the Island isn't able to import it.

As a user, if I rename my plugin or decide to exclude it, I can't import the rest of the saved configuration. I either have to reenter everything in the UI, or manually change the configuration file and import it.

## To Reproduce
Steps to reproduce the behavior:
1. Add a plugin to the data directory
2. Enable it in the configuration in the UI, submit, and export the configuration
3. Stop the Island, remove the plugin from the data directory, and restart the Island
4. Try to import the saved configuration
5. See error that it couldn't be imported

## Expected behavior
We should find a better way to communicate that a plugin wasn't found where it should've been, like a list of plugins that it couldn't find. The rest of the configuration should be imported.

## Screenshots