Add an option to hide the none selected text

[lionel-bijaoui]

As a solution to #210, I added an option hideNoneSelectedText in selectOptions

{			
	type: "select",
	label: "Role",
	model: "role",
	required: true,
	selectOptions: {
		hideNoneSelectedText: true
	},
	values: [{
		id: "admin",
		name: "Administrator"
	}, {
		id: "moderator",
		name: "Moderator"
	}, {
		id: "user",
		name: "Registered User"
	}, {
		id: "visitor",
		name: "Visitor"
	}],
	styleClasses: "half-width",
	validator: validators.required
}

[icebob]

Thanks! Mergeable