select-kit initial plugin api implementation (0.8.13)

```
api.modifySelectKit("identifier-of-the-select-targeted")
  .modifyContent((context, existingContent) => {})
  .appendContent(() => {})
  .prependContent(() => {})
  .onSelect((context, val) => {});
```

app/assets/javascripts/select-kit/components/multi-select.js.es6

@@ -2,6 +2,9 @@ import SelectKitComponent from "select-kit/components/select-kit";
 import computed from "ember-addons/ember-computed-decorators";
 import { on } from "ember-addons/ember-computed-decorators";
 const { get, isNone, isEmpty, makeArray } = Ember;
+import {
+  applyOnSelectPluginApiCallbacks
+} from "select-kit/mixins/plugin-api";
 
 export default SelectKitComponent.extend({
   pluginApiIdentifiers: ["multi-select"],
@@ -81,10 +84,14 @@ export default SelectKitComponent.extend({
     Ember.run.next(() => {
       this.mutateContent(this.get("computedContent"));
       this.mutateValues(this.get("computedValues"));
+      applyOnSelectPluginApiCallbacks(this.get("pluginApiIdentifiers"), this.get("computedValues"), this);
       this.set("headerComputedContent", this.computeHeaderContent());
     });
   },
-  mutateValues(computedValues) { this.set("values", computedValues); },
+  mutateValues(computedValues) {
+    this.set("values", computedValues);
+  },
+  mutateContent() { },
 
   filterComputedContent(computedContent, computedValues, filter) {
     const lowerFilter = filter.toLowerCase();

app/assets/javascripts/select-kit/components/select-kit.js.es6

@@ -1,10 +1,12 @@
-const { isNone, run, makeArray } = Ember;
+const { isNone, makeArray } = Ember;
 import computed from "ember-addons/ember-computed-decorators";
 import UtilsMixin from "select-kit/mixins/utils";
 import DomHelpersMixin from "select-kit/mixins/dom-helpers";
 import EventsMixin from "select-kit/mixins/events";
 import PluginApiMixin from "select-kit/mixins/plugin-api";
-import { applyContentPluginApiCallbacks } from "select-kit/mixins/plugin-api";
+import {
+  applyContentPluginApiCallbacks
+} from "select-kit/mixins/plugin-api";
 
 export default Ember.Component.extend(UtilsMixin, PluginApiMixin, DomHelpersMixin, EventsMixin, {
   pluginApiIdentifiers: ["select-kit"],
@@ -81,7 +83,7 @@ export default Ember.Component.extend(UtilsMixin, PluginApiMixin, DomHelpersMixi
   willComputeContent(content) { return content; },
   computeContent(content) { return content; },
   _beforeDidComputeContent(content) {
-    content = applyContentPluginApiCallbacks(this.get("pluginApiIdentifiers"), content);
+    content = applyContentPluginApiCallbacks(this.get("pluginApiIdentifiers"), content, this);
 
     const existingCreatedComputedContent = this.get("computedContent").filterBy("created", true);
     this.setProperties({
@@ -91,16 +93,6 @@ export default Ember.Component.extend(UtilsMixin, PluginApiMixin, DomHelpersMixi
   },
   didComputeContent() {},
 
-  mutateAttributes() {
-    run.next(() => {
-      this.mutateContent(this.get("computedContent"));
-      this.mutateValue(this.get("computedValue"));
-      this.set("headerComputedContent", this.computeHeaderContent());
-    });
-  },
-  mutateContent() {},
-  mutateValue(computedValue) { this.set("value", computedValue); },
-
   computeHeaderContent() {
     return this.baseHeaderComputedContent();
   },

app/assets/javascripts/select-kit/components/single-select.js.es6

@@ -1,7 +1,10 @@
 import SelectKitComponent from "select-kit/components/select-kit";
 import { on } from "ember-addons/ember-computed-decorators";
 import computed from "ember-addons/ember-computed-decorators";
-const { get, isNone, isEmpty, isPresent } = Ember;
+const { get, isNone, isEmpty, isPresent, run } = Ember;
+import {
+  applyOnSelectPluginApiCallbacks
+} from "select-kit/mixins/plugin-api";
 
 export default SelectKitComponent.extend({
   pluginApiIdentifiers: ["single-select"],
@@ -44,6 +47,19 @@ export default SelectKitComponent.extend({
     });
   },
 
+  mutateAttributes() {
+    run.next(() => {
+      this.mutateContent(this.get("computedContent"));
+      this.mutateValue(this.get("computedValue"));
+      applyOnSelectPluginApiCallbacks(this.get("pluginApiIdentifiers"), this.get("computedValue"), this);
+      this.set("headerComputedContent", this.computeHeaderContent());
+    });
+  },
+  mutateContent() {},
+  mutateValue(computedValue) {
+    this.set("value", computedValue);
+  },
+
   _beforeWillComputeValue(value) {
     switch (typeof value) {
     case "string":