Use custom IdM identity service in Flowable for user's groups resolution.

[krausvo1]

• IdM identity service for Flowable (former Activiti) has existed in Wren:IDM for some time, but it was never used. This PR refactors the service and group query implementation and enables usage of custom IdM service.
• IdM service refactor is based on Flowable's implementation of LDAP IdM identity service (flowable-ldap module, flowable-ldap-configurator module).
• Former group query implementation ignored filtering parameters. Not all parameters are supported. Only parameters that might be used by Flowable's internals or parameters used by Wren:IDM are supported.
• Main use case for these changes is letting Flowable handle resolution of group members when deciding whether user is a task candidate or not. We no longer need to check user's authzRoles and compare them with task's candidate groups manually. This is reflected by changes in router-authz.js, getavailableuserstoassign.js and gettasksview.js.

Other notable changes:

• endpoint/getavailableuserstoassign now should be called as query instead of action. The only script that calls this endpoint is gettasksview.js that incorrectly called it as query, which I think does make sense. Format of the response also changed: { users: [<users>], assignee: <assignee> -> [<users>]. Assignee property has not been used anywhere so I don't think it needs to preserved. Task's assignee is always available in the task instance object anyway.
• endpoint/gettasksview and custom authz functions canUpdateTask and isUserCandidateForTask no longer use user's authorization roles from security context to compare them with task instance's candidate groups. Instead, task instance resource is queried with appropriate query parameters (taskCandidateUser, taskCandidateOrAssignee) and Flowable will decide whether user is a candidate or not based on user's roles (reverse attribute for managed role's members attribute).
• User query used by IdM identity service has been disabled (throws error if used) since it is not used by Wren:IDM nor Flowable's internals (in Wren:IDM's use cases). I have not deleted IdmUserQuery.java, but I think we should consider it.

There are also some minor fixes that might be separated to another PR if desired.

[krausvo1]

Updated forgotten copyright headers.

[pavelhoral]

LGTM