Backend urls

By default SDK uses multiple urls for backend api calls and fallback to different url when some error happen.

First it uses urls passed to ClientInfo#addUrls and ClientInfo#addUrl

Then default urls integrated to the sdk

To override these default urls add new raw resource to your project with name pango_default_urls.json

Follow the structure

{  
    "primary": [    
        "https://url-1.net",    
        "https://url-2.com",    
        "https://url-3.com"  
    ]
}

You can change the urls or specify primary array as empty to keep only ClientInfo urls