Fix the duplicate show-password element ids.

* change one to 'show-old-password', the other to 'show-new-password'

fixes #340

app/scripts/templates/change_password.mustache

@@ -11,9 +11,9 @@
     <div class="input-row password-row">
       <input type="password" class="password" id="old_password" placeholder="{{#t}}Old password{{/t}}" pattern=".{8,}" autofocus required>
 
-      <label for="show-password">
+      <label for="show-old-password">
         <span class="show-password-label-text">{{#t}}Show{{/t}}</span>
-        <input id="show-password" type="checkbox" class="show-password">
+        <input id="show-old-password" type="checkbox" class="show-password">
       </label>
 
     </div>
@@ -21,9 +21,9 @@
     <div class="input-row password-row">
       <input type="password" class="password" id="new_password" placeholder="{{#t}}New password{{/t}}" pattern=".{8,}" required>
 
-      <label for="show-password">
+      <label for="show-new-password">
         <span class="show-password-label-text">{{#t}}Show{{/t}}</span>
-        <input id="show-password" type="checkbox" class="show-password">
+        <input id="show-new-password" type="checkbox" class="show-password">
       </label>
 
       <div class="input-help">{{#t}}Must be at least 8 characters{{/t}}</div>