Replace use of commons-logging with slf4j
commons-logging is used although we should use the logging facade slf4j
so we are independent of the actual logging implementation of
openmrs-core. commons-logging is actually excluded from the
openmrs-core dependencies but somehow kreeped in.
* replace usage of commons-logging with slf4j
* add rule to checktsyle.xml to flag imports of commons-logging
as illegal
* order imports according to eclipse default, remove unused imports
