Split up ami.py and added logging

Split up ami.py into --

ami.py -- top level control of digital system as a whole
roach.py -- FpgaClient subclass with extra methods
engines.py -- Engine, FEngine and XEngine classes

Added logging. Default configuration is generated by helpers and includes
logging to stdout, redis subscription channel 'log-channel' and syslog.

Removed print statements and verbose switches in favour of logging calls.