Client: async resources, make store reusable, move plugins and add getTaskFor getter (#8575)

Add library to manage async resource
Make Store reusable for easier testing
Move plugin to libs
Add getTaskFor getter with tests

website/client/libs/store/helpers/internals.js

@@ -0,0 +1,32 @@
+/* Flatten multiple objects into a single, namespaced object.
+
+Example:
+
+  getters
+    user
+      gems
+      tasks
+      ...
+    tasks
+      todos
+      dailys
+      ...
+
+  Result:
+    getters
+      user:gems
+      user:tasks
+      tasks:todos
+      tasks:dailys
+*/
+export function flattenAndNamespace (namespaces) {
+  let result = {};
+
+  Object.keys(namespaces).forEach(namespace => {
+    Object.keys(namespaces[namespace]).forEach(itemName => {
+      result[`${namespace}:${itemName}`] = namespaces[namespace][itemName];
+    });
+  });
+
+  return result;
+}