API keys are now only visible when first created. After that, only the first four characters are stored in the database for identification, along with an sha256 hash of the full key. This makes key usage easier to audit, and ensures attackers would not have access to the live site in the event of a database leak.
This makes the merge lower risk, because we have some time to revert if needed. Once the change is confirmed to be working, we will add a second commit to drop the `key` column.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
