Toolbar supports iconSclass

Use Case

Since ZK 9 bundles Font Awesome 4.7 icons by default, it's better to provide a convenient way to add Font Awesome icons easily like setIconSclass(). ZK LabelImageElement/Toolbarbutton already supports such API.

So that application developers can have lots of built-in icons to use, no need to create or hunt from the web. For example,

ToolbarButton.Builder.create(ACTION_KEY).withIconSclass("z-icon-paperclip").withTooltip("attach file").withLabel("attach").build()