test(case/processTask): add assertions

related to CAM-2371
chore(qa): add freemarker template engine to distros

- remove dependencies of qa runtimes

related to #CAM-2449
test(case/caseTask): add assertions

related to CAM-2444
feat(engine/forms): provide form variables api

Provide improved access to form variables.
- Get form variables for start forms and task forms.
- takes into account form data specified using form fields
- returns Map of VariableInstance rather than map of raw value
  objects. The VariableInstance provides access to errorMessage as
  well as variableType information.

related to #CAM-2436
feat(engine): add script as possible execution listener

- an execution listener can have a camunda:script child which will
  be evaluated as execution listener
- the resource attribute is also supported for the script element

related to #CAM-2360
refactor(UI-TEST): implement page objects

This commit refactors the webapp UI test suite for page object
introduction.
test(UI-TEST/admin): add groups page tests
test(UI-TEST/admin): add admin user setup test