*.png files moved to directory images/
small code improvements
proto_xboard.cc: Don't include network.h
moved network.cc and network.h to direcotry network/
network.*: corrected include paths after movement
network: fallbackconnection class split into separate files
util.cc: tiny readability improvement
include path fixes
Makefile: Path fixes
network: Move implementation of connection classes to individual .cc files
So far it's easier to keep everything in network.h, so this partially
reverts previous commit (fallbackconnection.h deleted).
Makefile adjustments