Before, `.Site.Params.Manifest` was required to activate
Web App Manifest. Now, it's optional. Still, `.Site.Params.Manifest`
highly recommended.
* Don't require .Site.Params.Manifest
* Order Web App Manifest properties by required type (except icons)
* Add default value to startUrl param [`/`]
* README.md: enhance Web App Manifest configuration section
* README.md: add table with Web App Manifest default values in Binario