create_project_and_push: allow any namespace of a project

[wonder-sk]

Right now, create_project_and_push API call only supports creation of projects under user's name. It would be good to improve it so that user can create project in other namespace (e.g. within an organisation). Right now this needs to be done with custom code which is not entirely trivial, e.g. to create and push myorg/myproject:

directory = '/home/user/myproject'
mc = MerginClient(...)
mc.create_project("myproject", is_public=False, namespace="myorg")
mp = MerginProject(directory)
mp.metadata = {"name": "myorg/myproject", "version": "v0", "files": []}
mc.push_project(directory)