Update MCR setup and teardown tasks

[x] Instead of explaining how to do things, link to the relevant wiki pages.
[x] Add a test that checks all the URLs in the task graphs? Maybe the BoxCast or Church Online Platform ones would be tough, but at least check the GitHub ones since those seem the most likely to change.
[ ] Highlight file system paths similarly to how URLs are highlighted?
[x] Add a task for updating the Vimeo video thumbnail.
[x] Add a task for deleting outdated assets on Planning Center.
- [x] Why not look for outdated local assets during teardown as well, rather than during setup (when it's busier)?

recc-tech / tech