Create widget-vue.js to chat with the Cat from any webpage

[pieroit]

Create a widget to easily chat with the cat from any website (and from the /chat page in the core - see #267 ).

The widget:

• can be installed in a simple html page by simply importing a js and a css
• contains only the necessary elements to chat: input box and messages until now
• attaches itself in a specific div, for example:
  <div id="cat-widget-vue.js" data-url="my-cat-url.com">`

This issue here only for reference, as the widget will live in its own repo:
https://github.com/cheshire-cat-ai/widget-vue