Notion Hook: get list of files.

Now Notion Hook allows you to list the files on Push.
To do so, create a personal access token on GItHub and specify the file format. For now, the only file format allowed is text-list, hopefully in the future I'll add csv and other file types.

Heavily inspired by @jitterbit https://github.com/jitterbit/get-changed-files

Solve #1

Full Changelog:
1.0...1.1