Add support for bundle specific configuration

I've created a proof of concept which lists relevant fields separately per bundle as well as an "all bundles" option, which is the default and works the same as it does now without any changes to config.

Before I refine the code for sharing I'd like some feedback on the approach. This is how the field list would present.

I'm looking at adding support for third party settings. I think this only makes sense per instance so can probably be included here as well.

I've added support for third party settings. To test, enable Photoswipe's submodule Photoswipe Dynamic Caption and configure.