send user command without config

[Nokitoo]

As discussed in mage/mage#249, we should be able to use the SDK to manually send user commands.

mageSDK.setEndpoint(
    'http://127.0.0.1:8080',
    'game'
);
mageSDK.sendCommand(
    'players.register',
    {
        username: 'test'
        password: 'qdsqdsqds'
    }
);