Added deactivation of users

[djotaku]

Tested that it works with the following code (anonymized my username/password):

async def main():
    client = AsyncClient(myserver", myaccount)
    response = await client.login(password=mypassword)
    print(response)
    print(client.access_token)
    deactivate_response = await client.deactivate("@testy2:myserver", client.access_token)
    print(deactivate_response)
    await client.close()

asyncio.get_event_loop().run_until_complete(main())

and got the responses: Logged in as myaccount, device id: an id. my access token the correct url and, finally,

id_server_unbind_result success

So, as long as Travis is OK with my code, I think we're good.

[poljar]

This has merge conflicts now, could you resolve them. Perhaps CI will wake up as well after that.

[djotaku]

OK, finally fixed conflicts. Hopefully Travis is cool with things.