Emonhub fails to start after update

[Robert.Wall]

Python3 for emonhub

emonPi/base update now includes updating emonhub to python3! The update process includes the installation of Python3 and dependencies as well as a call to apt-get update which can take a little time on slower connections. The emonPiLCD script and service-runner are still ran with Python 2.7 which remains on the system. Thanks @bwduncan and @borpin for all of your help with this!