Specify library icons for start and end

Objective To specify library icons for startingIcon and endingIcon on a Button

To achieve this, consider the following steps:

1. To specify library icons in shorthand notation for startingIcon and endingIcon on a Button, you can use the following syntax:

   Button:
       startingIcon: wifi
       endingIcon: addressBook fontAwesome
2. Icons can be represented with a more verbose syntax on a Button using the following structure:

   Button:
       endingIcon:
           name: addressBook
           library: fontAwesome
           size: 50
           color: red