This PR replaces broccoli-file-remover with broccoli-funnel (https://github.com/broccolijs/broccoli-funnel) which allows excluding files from the tree using regular expressions.

We wanted to exclude all .map files, but they are automatically generated and there didn't seem to be a way to use the existing broccoli-file-remover with a glob/wildcard pattern.

This allows something like this to correctly remove index.html and any .map files from the output:

    manifest : {
      enabled: true,
      appcacheFile: "/manifest.appcache",
      excludePaths: ['index.html', new RegExp(/.\.map$/)],
      includePaths: [''],
      network: ['*']
    },

Thoughts?