Add hkps support
Fix url building to support certificate check on hkps servers

Note: the CA used by sks-keyservers.net is not valid for android, thus using hkps fails for them. pgp.mit.edu uses a perfectly valid cert.
Download from origin during ACTION_DOWNLOAD_AND_IMPORT_KEYS
Make abstract methods in Keyserver public (implementations make them public anyway)
Store nice origin with keybase keys (that can't be interpreted as HKP server)
Merge branch 'hkps-support' into automatic-contact-discovery
Merge ACTION_DOWNLOAD_AND_IMPORT_KEYS and ACTION_IMPORT_KEYBASE_KEYS