default sign-in dialog configuration

[johnbrosowsky]

Web AppBuilder is great for making small focused apps enabling real people to get work done using maps.  Often end users of WAB apps are not trained Esri ArcGIS Online professionals.  Therefore the default sign-in is highly confusing to users. The request is for the following:

• add a supported ability to replace the text "please sign in to access the item on ArcGIS Online" and the 32 char hexadecimal item id with the web application name and a logo
• add optional  "forgot password' link at the bottom  
• there are some unsupported CSS hacks that can help a little but not for things like adding a forgot password link button