Serve directly webchat widget from Masdif instead of refering to CDN

[lumpidu]

We want to have direct control of the webchat widget version that is served from Masdif.

• This version of the webchat widget is the compiled version webchat.umd.production.min.js as of commit https://github.com/SDiFI/webchat/tree/e254834621577b320627e30f177b53fde06803fe
• Move the javascript_tag and Webchat initialization code into the HTML head section instead of the body.
• add feedback initialization to Webchat widget construction
• Add more documentation inside README.md