rename maven artifacts for clarification (now: org.ws4d.jcoap.core, org.ws4d.jcoap.examples, org.ws4d.jcoap.proxy)
jcoap.core: removed jUnit4 dependency from classpath; was already part of maven build
jcoap.examples: removed jcoap.core project dependency from classpath; added dependency to maven build

moved to maven build; changed to log4j2 aligned package structure to jcoap.core; adapt to jcoap.core changes