Small tidy-ups

[Jaffa]

While getting familiar with the code, I found a number of small issues:

1. The frame size is set in avs/main.py for using hotwords, and in avs/check.py, but not in avs/alexa.py.
2. The examples for setting up valid callback URLs - for example https://github.com/alexa/alexa-avs-sample-app/wiki/Create-Security-Profile use localhost, not 127.0.0.1
3. There's a hardcoded ReSpeaker client ID & secret, which means if the user doesn't pass in config.json, they'll end up authorising your account by accident.

[xiongyihui]

The hardcoded ReSpeaker client ID is a feature for these who just want to try Alexa as quick as possible.

[Jaffa]

The hardcoded ReSpeaker client ID is a feature for these who just want to try Alexa as quick as possible.

OK, makes sense. Could I suggest one of the following:

1. A warning and/or explicit approval? Perhaps with an input
2. Move it into an example config.json?