Update the donors FAQ

Closes: #35 (closed)

The donor FAQ has been updated, and a new /refund-policy page has been added.

I moved away from the child pages to use flowblocks instead. The flowblocks simplify things a lot, the faq template delegates rendering the FAQ entries to a flowblock template, and there's now just a single contents.lr file for the entire FAQ. No more needing to create a new directory named something like 25-faq-name-here! This should also speed up the build time a little bit.