Description of problem:
Now there is no simple way how to create an ad-hoc task using REST or JMS.

Version-Release number of selected component (if applicable):
6.0.1 ER2

Steps to Reproduce:
1. Try to create a new ad-hoc task remotely using REST or JMS.
2. See that AddTaskCommand takes as a parameter Task object.

Actual results:
To create an instance of Task class you have to use TaskImpl class that is "internal" class and is not part of the jBPM 6 API. You also have to initialize a lot of its attributes (and their attributes recursively) to be able to successfully create a new ad-hoc task.

Expected results:
AddTaskCommand (or the new one) should take as parameters some basic information that is needed to create an ad-hoc task. They can be similar to the parameters of the addTask method in QuickNewTaskPresenter (https://github.com/droolsjbpm/jbpm-console-ng/blob/master/jbpm-console-ng-human-tasks/jbpm-console-ng-human-tasks-client/src/main/java/org/jbpm/console/ng/ht/client/editors/quicknewtask/QuickNewTaskPresenter.java#L116).

Additional info:
It should be considered not only adding a new command class which will simplify the creation of an ad-hoc task but also creating a new method directly in the TaskService.