explicitly set i2p.dir.base and i2p.dir.config in router.config for Docker containers. fixes and closes #41.

Automatically configure clients and client tunnels to listen on the container network address instead of the localhost. Closes #358

* disable in-network updates
* persistent directory for snark downloads
* listen on port 12345 for i2np connections
* restore multi-stage build
* use better ant target
* allow passing -Xmx via the JVM_XMX variable

Many thanks to LoveIsGrief for the suggestions!

add SSH tunnel for gitssh.idk.i2p services to i2ptunnel.config files for docker and regular installs

The follow clients and tunnels are available on all interfaces (0.0.0.0) of the container:

 - routerconsole
 - SAM
 - I2P HTTP Proxy
 - Irc2P