PmAttrListImpl: Default values are now only applied if the user did not
change the attribute value manually to an empty list.
javadoc
Merge commit 'f6c155acc4a58e421ea6f'

Conflicts:
	pm4j-core/src/main/java/org/pm4j/core/pm/impl/PmAttrListImpl.java
	pm4j-core/src/test/java/org/pm4j/core/pm/PmAttrListTest.java