chore(cockpit): add client side test infrastructure

Add infrastructure to test the cockpit client application via karma.

To test the cockpit client application proceed as follows:

- install karma (>=  0.9.2) via `npm -g install karma@canary`
- from within cockpit-webapp:
  - run cockpit via `mvn clean tomcat:run -Pdev`
  - start karma via `karma start src/test/js/config/karma.e2e.js`
  - execute single karma test run via `karma run`
refactor(cockpit core): add abstract engine aware

Class org.camunda.bpm.cockpit.service.AbstractEngineAware may be used to
implement engine aware cockpit services and resources.
feat(rest): add PATCH process instance variables

- adds a new command to the engine that allows updating and deleting
variables during one transaction

contributes to CAM-642
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
feat(rest): add GET, PUT, DELETE for single variables

contributes to CAM-642
chore(rest): change error status codes for variable methods

- from 400 to 500 in case of ProcessEngineException

contributes to CAM-642
test(rest): add execution query test

- does not add implementation

contributes to CAM-637
feat(rest): add execution query

- adds an ExectionRestService on /execution

contributes to CAM-637
refactor(rest): refactor common query functionality
docs(rest): add missing license headers
feat(cockpit): add failure chain query

Added FailureService that provides process definitions with failures

- Test cases altered to use UUID generator
- org.camunda.bpm.cockpit.plugin.test.AbstractCockpitPluginTest integrates
  with engine logging facilities now
- Some test cases are commented out (@Ignore) due to engine bug

Related to CAM-706
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
feat(rest): make execution rest service engine-addressable

contributes to CAM-637
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
feat(rest): add GET execution method

- GET /execution/{id}

contributes to CAM-638
feat(rest): add signal execution method

- POST /execution/{id}/signal

contributes to CAM-638
fix(cockpit api): fix AbstractEngineAware api visibility
feat(wink): support Apache Wink JAX-RS runtime

wink needs the Produces / Consumes annotation on method level

related to CAM-105
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
fix(ExceptionHandler): add media type to exception handler

this will make sure the rest implementation knows which
MessageBodyWriter to pick

related to CAM-105