Some bug-fixes and improvements

Most of the code is copied from sysfspusher and adapted to match perfpusher
TODO: think of a suitable config-file-layout
TODO: insert new code to read perf-counters

Outsourcing of sysfspusher.cpp into multiple classes is now complete

Minor fixes to SYSFSSensor

Sensors are now an own class as well.
Adapt Makefile accordingly.
It is now possible to define default sysfsSensors in the config.
See sysfspusher.conf for an example.

Move configuration parser to new class Configuration. Add configuration parameters for IPMI session timeout and retransmission timeout.