[BZ-1043395] fix recognition of formulas and free form expressions

(cherry picked from commit 9082ebc0a528a182b3ee4e9c58793be90ec82df3)

Conflicts:
	drools-workbench-models/drools-workbench-models-commons/src/test/java/org/drools/workbench/models/commons/backend/rule/RuleModelDRLPersistenceUnmarshallingTest.java