Missing:
-Certificate validation and so on required?
-just send request.xml? or use GET or something?
-undefined symbol error when trying to load plugin

2 Bugfixes:
-correct initialization of PDUSensors with new()
-cooldown value for XML-file refresh is now correctly converted from MS to NS

Remaining TODOs:
network logic to obtain XML-file
use appropriate lock when sensor accesses PDUUnit
make reading XML more generic?
Test it!