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

test/client/unit/specs/libs/i18n.js

@@ -0,0 +1,19 @@
+import i18n from 'client/libs/i18n';
+import commoni18n from 'common/script/i18n';
+import Vue from 'vue';
+
+describe('i18n plugin', () => {
+  before(() => {
+    Vue.use(i18n);
+  });
+
+  it('adds $t to Vue.prototype', () => {
+    expect(Vue.prototype.$t).to.be.a.function;
+  });
+
+  it('$t is a proxy for common/i18n.t', () => {
+    const result = (new Vue()).$t('reportBug');
+    expect(result).to.equal(commoni18n.t('reportBug'));
+    expect(result).to.equal('Report a Bug');
+  });
+});