Add API for overwriting default components (#850)

* implement API for overwriting child components

* add test coverage

* update documentation for Components & Styling

* update docs

* refactor API, update docs

* remove the service worker

* fix tests

tests/unit/Components.spec.js

@@ -0,0 +1,30 @@
+import Vue from 'vue';
+import { selectWithProps } from '../helpers';
+
+describe('Components API', () => {
+
+  it('swap the Deselect component', () => {
+    const Deselect = Vue.component('Deselect', {
+      render (createElement) {
+        return createElement('button', 'remove');
+      },
+    });
+
+    const Select = selectWithProps({components: {Deselect}});
+
+    expect(Select.contains(Deselect)).toBeTruthy();
+  });
+
+  it('swap the OpenIndicator component', () => {
+    const OpenIndicator = Vue.component('OpenIndicator', {
+      render (createElement) {
+        return createElement('i', '^');
+      },
+    });
+
+    const Select = selectWithProps({components: {OpenIndicator}});
+
+    expect(Select.contains(OpenIndicator)).toBeTruthy();
+  });
+
+});