the client doesn't hold the task manager anymore, instead it is now a
singleton that all objects dump their tasks into to be managed.
This allows to better separate the responsibilities of the various
virtual-objects. The client now is also a module-singleton which allows
us to remove that ugly global variable.
fixup: uses relative imports instead that absolute ones with Codemp in front.
rename of codemp_client.py into just client.py
Former-commit-id: 4a0cc20e82f9631931ba2f61379a61c461b1f291
