Adding feature to customize IPMI sensors name

These feature allows the user to add a customized name for the IPMI sensor.
Next to a sensor name, insert the customized sensor name as follows:

Sensor "Real Sensor Name;Custom Sensor Name"

NOTE:
I had to do some nasty things to file src/utils_format_graphite.c to
make everything work with a compliant sensor name. This MUST be changed
in future versions
Adding 'IgnoreSensorFail' option so that sensors are not removed

If option 'IgnoreSensorFail' is set to true, then sensors are not removed when
one single reading fails. Default value is false.