Unbundle playground

[benjaoming]

The package playground is unused:

➜  ka-lite git:(dist-packages) ack-grep --python playground kalite
kalite/basetests/tests.py
222:        "playground": NO_VERSION,
➜  ka-lite git:(dist-packages) ack-grep --python playground python-packages
python-packages/fle_utils/build/management/commands/generate_blacklist.py
67:            "python-packages/playground",

python-packages/playground/test_tools/mount_branch.py
11:import playground
12:from playground.docker.docker import Docker, PersistentDocker
13:from playground.utils.testing import lexec, get_open_ports
626:            self.dockers[server_type].run_command("cd /playground", wait_time=0.1)
632:            docker.run_command("export PYTHONPATH=${PYTHONPATH}:/playground", wait_time=0.1)
633:            docker.stream_command("python /playground/test_tools/mount_branch_on_docker.py %s %s %s %d %s" % (self.git_user, self.repo_branch, server_type, self.docker_port, self.git_repo), wait_time=wait_time)
691:#        self.docker.run_command("/playground/test_tools/mount_docker_branch.sh %s %s %s" % (self.git_user, self.git_repo, self.repo_branch))
802:    kap.mount_project(server_types=server_types, host="playground.learningequality.org")