Basic Authentication Support

[alexlobanov]

Hi,

Thanks for this awesome package.

This PR contain new feature - Basic authentication Support for webpages.
You will able to set UserName and Password from XAML Bindings or C#.

Change Log:

• Implemented Basic Auth support on iOS and Android platforms
• Added comments/documentation on the code side
• Added TEST case on Sample Project
• Updated documentation

XAML usage example:

<webview:FormsWebView x:Name="internetContent" 
                  Username="BasicUsername"
                  Password="BasicPassword"
                  ContentType="Internet"
                  Source="https://example.com/" />

C# usage example:

FormsWebView WebView = new FormsWebView() {
    ContentType = WebContentType.Internet,
    Source = "http://www.somewebsite.com",
    Username = "basicAuthUser",
    Password = "basicAuthPassword"
}

[mdima]

:D is seems a duplicate of this: #122

[alexlobanov]

@mdima yeah, started work on it before taking a look on PR :)

[mdima]

Eh... you know, I just returned from Minsk, I stayed there 3 weeks this month...

[svenfulen]

Can we PLEASE merge this?