DEV: Fix all 'require-valid-alt-text' lints except in reused compoments

Three violations require parameters from the caller to generate valid alt text.

app/assets/javascripts/admin/templates/badges-index.hbs

@@ -1,6 +1,6 @@
 {{#d-section class="current-badges"}}
   <div class="badge-intro admin-intro">
-    <img src={{badgeIntroEmoji}} class="badge-intro-emoji">
+    <img src={{badgeIntroEmoji}} class="badge-intro-emoji" alt={{i18n 'admin.badges.badge_intro.emoji'}}>
     <div class="content-wrapper">
       <h1>{{i18n "admin.badges.badge_intro.title"}}</h1>
       <div class="external-resources">

app/assets/javascripts/admin/templates/customize-themes-index.hbs

@@ -1,5 +1,5 @@
 <div class="themes-intro admin-intro">
-  <img src={{womanArtistEmojiURL}}>
+  <img src={{womanArtistEmojiURL}} alt={{i18n "admin.customize.theme.themes_intro_emoji"}}>
   <div class="content-wrapper">
     <h1>{{i18n "admin.customize.theme.themes_intro"}}</h1>
     <div class="create-actions">

app/assets/javascripts/admin/templates/emojis.hbs

@@ -31,7 +31,7 @@
       <tbody>
         {{#each sortedEmojis as |e|}}
           <tr>
-            <th><img class="emoji emoji-custom" src={{e.url}} title={{e.name}}></th>
+            <th><img class="emoji emoji-custom" src={{e.url}} title={{e.name}} alt={{i18n "admin.emoji.alt"}}></th>
             <th>:{{e.name}}:</th>
             <th>{{e.group}}</th>
             <th>