More feedback when adding OpenPGP key to WhisperBack report

reported by user, confirmed by me:

Users don’t feel the GPG key was added to WhisperBack.

Steps to reproduce:

- Open whisperback
- Add gpg key

There is no feedback about the key being good, or added.

The user is worried and cannot report to us because feels our answer will be unencrypted.

What should happen instead:

Some message about the key being added.

Original created by @emmapeel on 11200 (Redmine)

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