* 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!

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

 - routerconsole
 - SAM
 - I2P HTTP Proxy
 - Irc2P

The range of 5k ports should be replaced by a more precise choice of ports.
It also pollutes the `docker inspect` output with 5k more lines.

ant needed to be updated to >1.9, but the old image used an old alpine
 with the max version of ant being 1.8.

The build is split into 2 phases to reduce the size of the image.
A builder makes the installer and installs it in one image.
The installed files are copied over to the actual result image.