Refactoring configuation and key management

The client and server handshaker class was loading keystore and
truststore. I removed this code, the store need to be given at
DTLSConnector creation.

It's removing clutter from the handshaker classes and help to understand
how/who/where the key are loaded (single responsability principle)

Removing setting in ScProperties

Removed default port:
In fact DTLS have no default port, this settign doesn't really make
sense.

Now you configure everything using the Java API of DTLSConnector
and DTLSConnectorConfiguration