Fix keyring error handling

[KarimPwnz]

This code is intended to fix how jrnl handles keyring errors: if keyring retrieval fails, the user is now asked to enter the password manually. Additionally, the message "Failed to retrieve keyring" is displayed if the keyring exists. (This fixes #1020.)

I've also generalized the keyring tests and implemented those relevant here.

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have tested this code locally.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.
• All tests pass.

[wren]

Both great PRs. Thank you!