* Added some basic guards to prevent multiple instances from running.
Specifically, a file "router.ping" in the install directory which is
written to once a minute - if that file exists and has been modified
within the last minute, refuse to start up. In turn, adjust the
service wrapper to wait a minute before restarting a crashed JVM.
* Create a "work" directory in the I2P install dir which Jetty will
use for all of its temporary files.
* Tell the browser not to cache most of the router console's pages.
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