Add counter for pending tasks to sensors. Wait until all tasks are finished before deconstructing anything

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

Add possibility to compile with symbol DEBUG (use "make debug")
Minor fixes and improvements to debug-output

Finished rework of sysfs-files.
Adapted and improved various other involved classes.
TODOs remaining:
-adapting Makefile for automated compilation of librarys
-solving runtime errors when trying to run dcdbpusher with sysfs

Removed no longer required files from SYSFSSensor
Renamed SYSFS to Sysfs
Introduce Configurator-base class, derive SysfsConfigurator from base-class