Use material ID instead of title + topic title for aggregating feedback

[hexylena]

this should be slightly more rewrite safe and we'll need to keep it up a little bit less...

i've converted the ones in the google sheet, we just need to move the replacement column two times left, and it'll be ready (should be done when this is merged to prevent issues.)

the other bonus of course is that the remapping in the future to a new material can be done automatically by looking through redirect_from and discovering previous IDs for a material (this is not currently implemented) whereas we don't have historical titles without walking the git history. So we'll never have to update this file again (hopefully.)

Also adds a new yaml formatted output (feedback2.yaml) that's a bit easier to walk through for a specific tutorial

---
introduction:
  galaxy-intro-101:
  - rating: 5
    pro: very detailed and easy to follow, even for a complete beginner - great!
    con:
    date: '2018-09-14'
    lang:
  - rating: 5
    pro:
    con:
    date: '2018-09-24'
    lang:
  - rating: 5
    pro:
    con:
    date: '2018-09-25'
    lang: