Allow babelified/'export default' resources to be fed into catalog/loader

[Cethy]

Use case:
During development of a (pre) loader for Catalog (@see discussion in #403), I stumble across some error when trying to feed a "babelified" React Component to the catalog/loader.

eg:

{
    test: /(\.catalog-builder\.yml)/,
    use: ['catalog/loader', 'babel-loader', 'my-custom-loader']
},

[jstcki]

Thanks and sorry for only getting back to you now! This is cool but does it also still work with HMR? I think you'd need to call require() in the module.hot.accept callback again instead of referencing the resource. So I'd probably revert to separate require calls but wrap the ES module check in a function that returns the module.

[jstcki]

The upcoming @catalog/markdown-loader now expects a Markdown string as input only, so this won't be supported and has to be implemented differently. Thanks anyway!