New version of the WebUI

[nicolargo]

Improve the look and feel of the current WebUI.

Here it is for the version 4.5.2:

https://github.com/nicolargo/glances/blob/v4.5.2/docs/_static/screenshot-web.png

[nicolargo]

First proposal (open to discussion): in the https://github.com/nicolargo/glances/tree/feature/issue3485-refactor-webui branch