Remove dnsjava module
Add minidns submodule
Switch to dnsjava
Add TlsHelper (designed to be used with sks-keyservers.net)

We can't use the AndroidPinning library for this, because it requires the certificate to be signed using a system CA, sks-keyservers.net uses there own CA
Add hkps support for sks-keyservers.net
Few fixes on hkps

TODO: Fix add as well
Merge branch 'hkps-by-default' of github.com:mar-v-in/open-keychain into hkps-by-default