First code of fetching GPG key from keyserver and adding bank.

This does not currently add keys but only the bank data from the key.
Assume the same file type for all files sent in a single message.
First code to import key using gpg tools and via keyservers.

Search, list and export keys from gpg. This will need some polish but
seems to work somewhat at least.
Fix key import.

Fix multiple small flaws in the key import.
- First, allow to have multiple keys matching the search query, prompt
  the user for which one to use.
- Add s to --export-secret-keys option used to remove possibility of
  ambiguity.
- Export the secret key really when we say we are doing it.
- Commit when we are done with all calls for an atomic add.