Added translatable plural forms to search as mentioned in pagekite/Mailpile#288.
Added one more pluralization.
Whoops, fixed a string.
Formatting change.
Used linter to find a few more syntax problems.
Extended error message on config decryption failure.

- Added version and binary used to exception message
- Should help troubleshooting issue #408
- Replaced direct gpg binary call with mailpile.crypto.gpgi.GnuPG interface.
Merge pull request #674 from mattcarberry/add_plural_translations

Add plural translations - #288
Merge pull request #694 from codeburg/issue_408_improve_error_message

Extended error message on config decryption failure.