preliminary debian package support

This sets i2p up as a functional Debian source package. dpkg-buildpackage
will build i2p using ant preppkg (tarball takes too long and not
helpful). It creates a binary .deb archive of the i2p installation,
which when installed goes into /var/lib/i2p as the non-root user i2p,
and adds an /etc/init.d script to start it up.

Some problems not yet solved:
1) under Debian the conf should go into /etc/i2p, but since it doesn't
   things like the eepsite index file get overwritten if you reinstall.
   should check for those somehow and not replace them, or ask the user.
2) under Debian they like it if you split the generated data from the
   static code, so i2p should go into /usr/lib/i2p maybe, but its
   netDB and any other cache files into /var/cache/i2p
   that's important not just for organization, but also /var is often
   on a filesystem optimized for churn. For now just put it in /var/lib
3) i2p is supposedly architecture independant, but it does choose a
   native jbigi library on postinstall, so does that really count
   as architecture independant?