feat: improve strings, challenges, and template readiness

app/assets/javascripts/views/challenge_modal/challenge-modal.pug

@@ -1,15 +1,15 @@
 .sk-modal-background(ng-click="ctrl.cancel()")
-.challenge-modal.sk-modal-content
+.challenge-modal.sk-modal-content(ng-if='ctrl.templateReady')
   .sn-component
     .sk-panel
       .sk-panel-header
-        .sk-panel-header-title {{ctrl.modalTitle}}
+        .sk-panel-header-title {{ctrl.challenge.modalTitle}}
       .sk-panel-content
         .sk-panel-section
           .sk-p.sk-panel-row.centered.prompt
-            strong {{ctrl.state.title}}
-          .sk-p.sk-panel-row.centered.subprompt(ng-if='ctrl.state.subtitle')
-            | {{ctrl.state.subtitle}}
+            strong {{ctrl.challenge.heading}}
+          .sk-p.sk-panel-row.centered.subprompt(ng-if='ctrl.challenge.subheading')
+            | {{ctrl.challenge.subheading}}
         .sk-panel-section
           div(ng-repeat="prompt in ctrl.state.prompts track by prompt.id")
             .sk-panel-row

app/assets/javascripts/views/challenge_modal/challenge_modal.ts

@@ -12,8 +12,6 @@ import { WebDirective } from '@/types';
 import { confirmDialog } from '@/services/alertService';
 import {
   STRING_SIGN_OUT_CONFIRMATION,
-  STRING_STORAGE_UPDATE,
-  STRING_AUTHENTICATION_REQUIRED,
 } from '@/strings';
 
 type InputValue = {
@@ -32,8 +30,6 @@ type ChallengeModalState = {
   showForgotPasscodeLink: boolean,
   processingPrompts: ChallengePrompt[],
   hasAccount: boolean,
-  title: string,
-  subtitle: string
 }
 
 class ChallengeModalCtrl extends PureViewCtrl<{}, ChallengeModalState> {
@@ -93,8 +89,6 @@ class ChallengeModalCtrl extends PureViewCtrl<{}, ChallengeModalState> {
       forgotPasscode: false,
       showForgotPasscodeLink,
       hasAccount: this.application.hasAccount(),
-      title: this.challenge.title,
-      subtitle: this.challenge.subtitle,
       processingPrompts: []
     });
     this.application.addChallengeObserver(
@@ -137,14 +131,6 @@ class ChallengeModalCtrl extends PureViewCtrl<{}, ChallengeModalState> {
     });
   }
 
-  get modalTitle(): string {
-    if (this.challenge.reason === ChallengeReason.Migration) {
-      return STRING_STORAGE_UPDATE;
-    } else {
-      return STRING_AUTHENTICATION_REQUIRED;
-    }
-  }
-
   async destroyLocalData() {
     if (await confirmDialog({
       text: STRING_SIGN_OUT_CONFIRMATION,