fix(bpmn): reference correct bpmnElement in bpmnPlane

related to #CAM-2928
chore(xslt-scripttask): update mvn pom and README.md

related to #CAM-2928
fix(stuff): upgrade engine, add dependency to spin, fix bpmn diagram

- upgrade camunda version to 7.2.0-alpha5
- add spin-core dependency since it is required now (was bundled in alpha3)
- fix bpmn diagram by matching id of process and bpmnPlane reference

related to #CAM-2927
refactor(rest-service): make artifactId unique and matching with content

This allows to import both projects (camunda-quickstart-soap-service &
camunda-quickstart-rest-service) into Eclipse.
impr(README): Add note about example
Update README.md