5.x: content sources are incorrectly output to the build output path

[cossssmin]

• Maizzle Version: 5.0.0-beta.18

There's currently a bug in the 5.x beta with the way we copy content sources to output paths, because we're trying to determine 'root' folders for each content source (which is a glob path) and it goes too high up, it's incorrect.

So if you have something like this:

export default {
  build: {
    content: [
      'src/templates/alerts/**/*.html',
      'src/templates/newsletter/**/*.html',
    ],
    output: {
      path: 'build_production',
    },
  }
}

You will get alerts templates in both build_production/alerts and at the root of build_production.

Since files are first copied over to the build.output.path, need to just copy over all files at the build.content paths correctly, preserving the structure.

Right now we're doing this relative to their 'root' directory so that we don't create build_production/src/templates/alerts/..., but this might need to change considering we now support content source glob paths.