Remove a leftover diagnostic log message.
Add the cryptokeys.getGetByName() interface.

Add openpgp_webcrypto_get_key(provider, name, id) and
openpgp_webcrypto_get_all_keys(provider), which uses a slight
extension of the WebCrypto Key Discovery protocol - getKeyByName(null)
that would return all the keys for the provider.

Add cryptokeys.getKeyByName() functions to all the supported providers:
- owncrypto already implements it with name != null, add a FIXME comment
  because it actually can fetch all the keys
- DOMCrypt has the capability to store a single key, so add a FIXME
  comment to implement it later
- NfWebCrypto does not have any key storage capabilities yet
Add the beginnings of a CryptoStick interface.

Support the cryptostick.webcrypto Mozilla extension that is still
under development; it currently only supports getKeyByName().

Add a trivial getKeyByName() test to signtest.js.