Add the option to set a icon for the toast title

[roalvesrj]

I added the option to set the icon option to the title.

Made changes to the .css and toast.js files (did not edit the .min.js file. I also made the changes to the sample file and readme.

In the icon sample file, I'm using the "Font Awesome" package classes, version 5 free. Therefore, to display the icon, you must include the package files.