Add version-checking feature (disallow old versions)

• cleanup fpn0 net scripts, remove extraneous ip cmd, fix verbose output
  • switch back from SNAT to MASQ for egress routing
  • restrict rp_filter manipulation to fpn0 iface
  • flush custom route table instead of cache on shutdown
• cleanup msg daemons, remove verbose output, use get_runtimedir for pid
  • set verbose=0 as default, remove extraneous log output
• add UPGRADE msg handling and do_shutdown func, add semver dependency
• add version to announce msg and version check to responder daemon
• update get_cachedir/get_runtimedir cmd output, update valid dirs
• update readme, add/update tests for new code and output changes