Use new kernel management modules

[takluyver]

Switch from jupyter_client to the new modules I'm working on: jupyter_kernel_mgmt and jupyter_protocol.

This means that the kernel to be tested no longer needs a kernelspec installed. By default it will still look for one, but you can override the launch_kernel classmethod to do something like this:

@classmethod
def launch_kernel(cls):
    from jupyter_kernel_mgmt.subproc import SubprocessKernelLauncher
    launcher = SubprocessKernelLauncher(['python', '-m', 'ipykernel', '{connection_file}'])
    return launcher.launch()

I made changes to both jupyter_kernel_mgmt and jupyter_protocol while working on this, so you probably want to get an updated version if you want to test it.

[rgbkrk]

Sweet.