Service-based remote shell

This version starts a service-based remote shell.

It does not drop the connection nor freeze on Home button pressed, but have no access to the mActivity:

```python
$ ssh -p8000 admin@192.168.0.14
admin@192.168.0.14's password:
>>> from jnius import autoclass, cast
>>> activity = autoclass('org.renpy.android.PythonActivity').mActivity
>>> activity is None
True
```

Do you think it is worth the benefit?