Bear: Do not inherit from Process

The Process class is not really useful and a Bear descendant will not be
executed as an own process.
ProcessSpawner: Do not inherit from Process

The Process class is not really useful and a ProcessSpawner will not be
used as a Process anyway.
ProcessSpawner: Remove Process dependency

Only a run method is needed. Enforcing some inheritance for this is not
really useful but rather blocking.
BearRunner: Don't inherit from Process

This inheritance is rather useless. See child commits of this one for
more info.
processes: Remove Process class

This class is not needed anymore. We can use multiprocessing.Process or
just ask for hasattr(obj, "run") to achieve the same.