Training site overhaul

[erinlynmclean]

• [x] Fix dead links on https://arcticdata.io/training/
• [ ] Add Google Analytics to https://training.arcticdata.io/
• [x] Link https://training.arcticdata.io/ to https://arcticdata.io/training/ so t hat people can access it from the website

[smerickson1]

test

[erinlynmclean]

@laurenwalker I don't know how to add Google Analytics to training.arcticdata.io - any help with that would be great!