chore(project): restructure project

This commit restructures the application into different subprojects

org.camunda.bpm.modeler.standalone.bundle -> the app
org.camunda.bpm.modeler.standalone.product -> the product
org.camunda.bpm.modeler.standalone.parent -> the standalone modeler root

In addition it facilitates tycho to build the product artifacts.
Generate them via `mvn clean verify` from with in the project root.

Closes #15
docs(CONTRIBUTE): update setup hints