add remote support via SSH

[WolfgangFahl]

The wikitask server should be able to manipulate a wiki on a remote server via ssh using ssh keys and e.g. tunneling the MySQL connection securely via SSH.

see

• http://www.jcraft.com/jsch/
• https://stackoverflow.com/questions/4932005/can-we-use-jsch-for-ssh-key-based-communication
• https://stackoverflow.com/questions/2003419/com-jcraft-jsch-jschexception-unknownhostkey
• https://stackoverflow.com/questions/30178936/jsch-sftp-security-with-session-setconfigstricthostkeychecking-no
• http://www.jcraft.com/jsch/examples/PortForwardingL.java
• https://stackoverflow.com/questions/199624/scp-via-java

for possible implementation options