All tasks should have a useful name attribute #127
Description
Currently Task has two "namey" attributes, .name which is either None or the explicitly-given name (e.g. @task(name='foo')), and __name__ which copies self.body.__name__ (so typically the name of a wrapped function.)
However, most code, and certainly the natural feeling API, is to always look at task_obj.name - which as above is going to be None a lot of the time if not explicitly given.
Switch it to a property that falls back to __name__ when name is not set.
