parent_data struct contains info that is common for each task,
not only in parent-child relationship context. To use it this way
without confusion, its name is changed to task_info.
In order to be able to widely and comfortably use task_info,
it is moved from tasks/task_manager.hh to tasks/types.hh
and slightly extended.
The implementation of a test api that helps testing task manager
api. It provides methods to simulate the operations that can happen
on modules and theirs task. Through the api user can: register
and unregister the test module and the tasks belonging to the module,
and finish the tasks with success or custom error.