Add BackgroundColor and VideoAutoplay to CefSettings

[russkyc]

This PR adds 2 things:

1. Allow for setting the background color of the webview using:

// Set cef background color
WebView.Settings.BackgroundColor = Color.Black; 

This should be useful for:

• Dark themed apps, so that the webview does not flash white while loading content
• Consistency, we will be able to set a background consistent with the content that will be loaded

2. Allow setting the video autoplay behavior using:

// Set cef video autoplay behavior
WebView.Settings.EnableVideoAutoplay = true;

Which should resolve #397

[heldergoncalves92]

May you add a summary comment explaining that on Color.FromArgb(alpha, r, g, b), background colors with alphas different from 255 are not supported by Cef?

[heldergoncalves92]

Hello @russkyc,

Thank you for the contribution! It’s great to have you helping out. Feel free to pick up any other open issues if you're interested in contributing further.