feat(webapp/test/util): provide a new camunda webapp test utility

This commit adds a new module called "camunda-webapp-test-utility" that
provides a "JobExecutorHelper" and a "DbSchemaPrefixTestHelper". Those can
be used inside custom plugins to write test cases which uses a JobExecutor
or to run the unit test against a db table prefix.

related to CAM-1798
chore(maven): use correct maven config tag
chore(maven): add ejb-client to central profile, bom inherits from parent
improve(grunt): rewording "production" into "dist"
feat(cockpit/candidate groups): add the ability to manage groups of a task

This commit adds a button in the user task table
who opens a modal window allowing to add or remove candidate groups to a user task.
For easier testing of that new feature a process definition called "User task identity links test 1"
with predefined groups, assignee and owners has been created.

Additional changes:
- A small directive providing a widget to edit, simple text variable, in place - like the name of asignee
- Adds some comments for jsdoc
- Improve the linting of some files

Closes CAM-1182
chore(qa): add postgresql 9.3 support

related to CAM-1592
fix(qa): add postgresql 9.3 support

related to CAM-1592
fix(bom): readd versions
refactor(cockpit/breadcrumbs): clean $rootScope from breadcrumbs

This commit also adds some comments for documentation generation with jsdoc and
improve the linting of some files.

Closes CAM-1779
fix(qa): increase timeout for webapp deployment
chore(db-db2): remove redundant columns for business key on db2

related to CAM-1515
impr(jobexecutor): remove exception if acquired job is deleted

The process engine should not throw an exception if an acquired Job is
deleted before it is actually executed. It should produce a Logging
message instead.

Related to #CAM-1842
Fix (engine-cdi): cdi local variables

ScopedAssociation.getVariable() cannot handle local variables

Related to CAM-1806
chore(engine-cdi): fixup formatting in CtxAssocMmanager
fix(engine): remove only in JobExecutor Context

make sure "no such Job Exception" is only remove in Job Executor Context

related to #CAM-1842
test(engine/history) document history level

relates to CAM-1844