Implement passcode functionality

There will come a time (maybe sooner than we expect) in which user's will want to protect their account with a Passcode, so starting an issue to track this. Obviously the copy, if it's part of a multi-step configuration, number of input digits (I personally like 4, but I understand 6, and don't have a strong opinion), etc.. could change, so feel free to suggest anything!

Obviously there will be other work necessary to make this happen, and might not be part of the MVP, will let @pavlenex determine what's best, but tracking + the app create/confirm/enter mocks nonetheless:

- [ ] Create Passcode
- [ ] Confirm Passcode
- [ ] Enter passcode