Router: Prep for RI sig types:

 - New router.sigType config
 - Generate / regenerate router keys based on config
 - New router.keys2 file format for sig types and padding
 - Fix RouterInfo.readBytes() signature verification with sig types
 - Catch unset padding in KeysAndCert.writeBytes()
 - Catch key errors in ReadRouterJob
 - Show RI sig type on /netdb in console
 - Move some things from Router to startup classes
 - Startup classes package private
 - Buffer readin of key files
 - Remove configurability of router.info and router.keys file locations