added "getLabelClasses" and unit test, using the fieldClasses unit test as an example

Author: zoul0813

src/fields/abstractField.js

@@ -176,6 +176,10 @@ export default {
 			return this.schema.fieldClasses || [];
 		},
 
+		getLabelClasses() {
+			return this.schema.labelClasses || [];
+		},
+
 		formatValueToField(value) {
 			return value;
 		},

test/unit/specs/fields/abstractField.spec.js

@@ -503,4 +503,28 @@ describe("abstractField.vue", function() {
 
 	});
 
+
+	describe("check classes application to labels", () => {
+		
+		let schema = {
+			type: "text",
+			label: "First Name",
+			model: "user__model",
+			inputName: "input_name",
+			labelClasses: ["applied-class", "another-class"]
+		};
+		let model = {};
+
+		before( () => {
+			createField(this, schema, model);
+		});
+
+		it("should have 2 classes ('applied-class' and 'another-class')", () => {
+			expect(field.getLabelClasses().length).to.be.equal(2);
+			expect(field.getLabelClasses()[0]).to.be.equal("applied-class");
+			expect(field.getLabelClasses()[1]).to.be.equal("another-class");
+		});
+
+	});
+
 });