cmake: add easyloggingpp download target
logger: introducing easyloggingpp
examples: example usage of new logger
logging: fix timestamp formatting and tweak setup
examples: introduce new logger also for other examples
logger: removing config file

replaced it by hard-coded configuration in header files tunable by
preprocessor defines prior to including the logging header
docu: adding some docu to logging functions
cmake: remove unneeded pp symbol; add warning to generatd site_config.hpp
Merge pull request #105 from torbjoernk/feature/logging

Introducing easylogging++ as versatile logging framework