Create a simple copy/paste string for quick mobile app registering

Currently, to ask a user to start using the Ombi app on their phone, they have to do so many steps that many users don't want to be bothered.
The plex login prompt doesn't appear in the new IOS app so they can't use that to login initially. Although they have the ability to point their phone at a QR code, this requires them to log onto Ombi on another machine and do many steps to be able to complete this. Again, too much work for many users.

The simplest and fastest way to get my users using Ombi is to:
- email them from within Ombi v4 with the following instructions:
- 1. Download it from the <linked>Play Store or <linked>App Store
- 2. Copy this code: <blah>
- 3. Start up the Ombi app
- 4. Paste the code into the app to complete the registration.
The code would be received by the Ombi server, matched against the user, and allow completion of the app login details. The code is then invalidated to prevent re-use.