[task] in gazu.task.get_task_type_by_name and new parameter for_entit…

[EvanBldy]

…y to allow to filter on task type with same name but different for_entity

Problem

• gazu.task.get_task_type_by_name : it's not possible to filter task types with same name but different for_entity / department (see here : gazu.task.get_task_by_name returns nothing #308).

Solution

• gazu.task.get_task_type_by_name : add new parameter for_entity / department by default to None, to allow filter on these columns.