Extract communicators for Create environments

[csherstan]

The DXL and UR5 environments have been updated to move the communicator setups outside the environments, instead they are now passed in as a parameter. The same needs to be done for the Create2 envs as well.

Affected files:
senseact/envs/create2/create2_docker_env.py
senseact/envs/create2/create2_mover_env.py
examples/advanced/create2_docker.py
examples/advanced/create2_mover.py