#4 Import/Export keys from clipboard

[hf]

Add command to import and export (public) keys via
clipboard.

I receive and send many public keys via e-mail, inline
as part of the text. I'd love to be able to just select
the public key and paste in in GPG Keychain (and vice
versa). This feature works already in Enigmail. I like
it a lot.

Inspiration for UI:
- Enigmail 0.89.5.0 OpenPGP Key Management

Aplies to GPG Keychain Access 0.7.0PB3