TODO: find a way to wait for all handlers dispatched by _strand to finish

Sensors which are part of an aggregating instance (e.g. in plugins PDU, IPMI, BACnet) now get a name prefix representing the agg. instance

Add possiblity to specify address_cache file for BACnet plugin in config (relies on BACnet-stack patch)

Next step: check correctness

Extend Makefile to compile BACnet plugin. Some bugfixes to BACnet files. However, there are still some compiler errors left to resolve

Implement logic for BACnetConfigurator (not yet tested). Induced slightly changes to bacnet.conf and BACnetClient

2 bugfixes (IPMI): take return value of ipmi_sensor_read into account; close sdrCache + ipmi-connection after reading