Introduces select-kit

* renames `select-box-kit` into `select-kit`
* introduces `single-select` and `multi-select` as base components
* introduces {{search-advanced-category-chooser}} as a better component for selecting category in advanced search
* improves events handling in select-kit
* recreates color selection inputs using {{multi-select}} and a custom {{selected-color}} component
* replaces category-selector by a component using select-kit and based on multi-select
* improves positioning of wrapper
* removes the need for offscreen, and instead use `select-kit-header` as a base focus point for all select-kit based components
* introduces a formal plugin api for select-kit based components
* introduces a formal pattern for loading and updating select-kit based components:

```
computeValue()
computeContent()
mutateValue()
```

test/javascripts/components/list-setting-test.js.es6

@@ -11,10 +11,26 @@ componentTest('default', {
   },
 
   test(assert) {
-    expandSelectBoxKit();
+    expandSelectKit();
 
     andThen(() => {
-      assert.propEqual(selectBox().header.name(), 'bold,italic');
+      assert.propEqual(selectKit().header.name(), 'bold,italic');
+    });
+  }
+});
+
+componentTest('with emptry string as value', {
+  template: '{{list-setting settingValue=settingValue}}',
+
+  beforeEach() {
+    this.set('settingValue', '');
+  },
+
+  test(assert) {
+    expandSelectKit();
+
+    andThen(() => {
+      assert.equal(selectKit().header.el.find(".selected-name").length, 0);
     });
   }
 });
@@ -27,10 +43,10 @@ componentTest('with only setting value', {
   },
 
   test(assert) {
-    expandSelectBoxKit();
+    expandSelectKit();
 
     andThen(() => {
-      assert.propEqual(selectBox().header.name(), 'bold,italic');
+      assert.propEqual(selectKit().header.name(), 'bold,italic');
     });
   }
 });
@@ -44,28 +60,28 @@ componentTest('interactions', {
   },
 
   test(assert) {
-    expandSelectBoxKit();
+    expandSelectKit();
 
-    selectBoxKitSelectRow('underline');
+    selectKitSelectRow('underline');
 
     andThen(() => {
-      assert.propEqual(selectBox().header.name(), 'bold,italic,underline');
+      assert.propEqual(selectKit().header.name(), 'bold,italic,underline');
     });
 
-    selectBoxKitFillInFilter('strike');
+    selectKitFillInFilter('strike');
 
     andThen(() => {
-      assert.equal(selectBox().highlightedRow.name(), 'strike');
+      assert.equal(selectKit().highlightedRow.name(), 'strike');
     });
 
-    selectBox().keyboard.enter();
+    selectKit().keyboard.enter();
 
     andThen(() => {
-      assert.propEqual(selectBox().header.name(), 'bold,italic,underline,strike');
+      assert.propEqual(selectKit().header.name(), 'bold,italic,underline,strike');
     });
 
-    selectBox().keyboard.backspace();
-    selectBox().keyboard.backspace();
+    selectKit().keyboard.backspace();
+    selectKit().keyboard.backspace();
 
     andThen(() => {
       assert.equal(this.get('choices').length, 3, 'it removes the created content from original list');