Classpath fixes

- `-Djava.library.path` needs to be set for resources like `libjbigi` to load.
- `-cp` needs to be set so the java `ClassLoader` can find classes.

With these changes, `jy2p.sh` is functionally equivalent to `runplain.sh` - it runs the full Java I2P router with routerconsole, I2PTunnel, plugins etc.