feat(formFields): Add cancel and esc handling and CTRL+Z to dialog.

- ModelerDialog contains the whole implementation for CRTL+Z, cancel and
  esc in dialogs
- add validation for mandatory fields
- make help text for mapping tables configurable

- "Form Fields" tab is now activated in the code base

related to #CAM-1398
fix(formFields/detailsDialog): Use no internal eclipse classes.

related to #CAM-1398
fix(callActivity/calledElement): Fix namespace for calledElement attribute.

closed #CAM-1510
fix(core): Fix NPE when participant have no processRef attribute.

closed #CAM-1497
fix(contexMenu): Delete unnecessary code

related to #CAM-1494
feat(tests): add abstract integration test base

This commit adds a new integration test case class to the modeler test
suite.

The AbstractIntegrationTest may be used to open, manipulate and save
a diagram in a modeler. It resambles the actual editor behavior as much
as possible.

A test case may use the API methods #open, #execute and #save to
interact
with the opened editor.

A simple integration test built on top of the new foundation is the
RoundtripTest.

Closes CAM-1496

Conflicts:
	org.camunda.bpm.modeler.tests/src/org/camunda/bpm/modeler/test/model/CreateSaveRoundtripTest.java
fix(AbstractIntegrationTest/Kepler): Use other save() method from graphiti

- method "save(final TransactionalEditingDomain editingDomain, final
  Map<Resource, Map<?, ?>> options)" from graphiti EmfService class is not
  supported in Kepler

related to #CAM-1496