add font family dropdown in ckeditor

1. Add font in build-config.js

plugins : {
	.........
    .......
	'font' : 1,
    ......
    .......
}

2. Then add font_name inside config.js

config.font_names = 'Arial;Times New Roman;Verdana';

reference :
https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_config.html#cfg-font_defaultLabel