the ombi password wasn't being changed w/ password resets initiated
through the admin page (and probably by other routes, too), as the code
was considering a HTTP 204 from Jellyfin as a failure, causing it to
skip anything with Ombi. Also added a little check for Ombi-imported
accounts that probably won't help with anything, but whatever.
Get/GetKey/SetKey/DeleteKey methods are used for access to
email/discord/telegram/matrix, everywhere. Mutex added for each, avoids
concurrent read/write issues. Will also make potential transition to
database easier.