FEATURE: Implement 2factor login TOTP

implemented review items.

Blocking previous codes - valid 2-factor auth tokens can only be authenticated once/30 seconds.
I played with updating the “last used” any time the token was attempted but that seemed to be overkill, and frustrating as to why a token would fail.
Translatable texts.
Move second factor logic to a helper class.
Move second factor specific controller endpoints to its own controller.
Move serialization logic for 2-factor details in admin user views.
Add a login ember component for de-duplication
Fix up code formatting
Change verbiage of google authenticator

add controller tests:
second factor controller tests
change email tests
change password tests
admin login tests

add qunit tests - password reset, preferences

fix: check for 2factor on change email controller
fix: email controller - only show second factor errors on attempt
fix: check against 'true' to enable second factor.

Add modal for explaining what 2fa with links to Google Authenticator/FreeOTP

add two factor to email signin link

rate limit if second factor token present

add rate limiter test for second factor attempts

app/assets/javascripts/admin/controllers/admin-user-index.js.es6

@@ -41,6 +41,11 @@ export default Ember.Controller.extend(CanCheckEmails, {
     return userPath(`${username}/preferences`);
   },
 
+  @computed('model.second_factor_enabled','model.can_disable_second_factor')
+  canDisableSecondFactor(secondFactorEnabled, canDisableSecondFactor) {
+    return secondFactorEnabled && canDisableSecondFactor;
+  },
+
   actions: {
 
     impersonate() { return this.get("model").impersonate(); },
@@ -63,6 +68,7 @@ export default Ember.Controller.extend(CanCheckEmails, {
     deleteAllPosts() { return this.get("model").deleteAllPosts(); },
     anonymize() { return this.get('model').anonymize(); },
     destroy() { return this.get('model').destroy(); },
+    disableSecondFactor() { return this.get('model').disableSecondFactor(); },
 
     viewActionLogs() {
       this.get('adminTools').showActionLogs(this, {