Login keys are sometimes unusable

[simonwex]

From email support:

When I click sign-up, I'm told my email has already been registered. When I used the "key" I was sent, I get a message saying that key is incorrect.

This could either be a UX issue or an issue with the key lookup.

Are we simplifying the keys before checking them against the DB? -- (e.g. trimming whitespace, removing inline whitespace, lower-casing, conflating "0" & "O")

This is a child of mozilla/id.webmaker.org#283