Decouple jbpm executor from CDI so it can be used with different frameworks

jbpm executor currently is bound to CDI even though it can be used without CDI although it is more difficult on EE containers which discovers CDI upon deployment which might cause issues for some frameworks - like CDI. Moreover if CDI is not used it does not make sense to introduce additional dependencies.

jBPM executor should follow same approach as jBPM services and provide:

• standalone core implementation which is framework independent
• cdi add ons for running in CDI environment - default for kie workbench
• ejb add ons for running in EJB container to allow async execution in embedded EJB application