Fix inconsistent capitalisation that resulted in unnecessary extra strings to translate

Thanks to @chimeno

wagtail/wagtailadmin/templates/wagtailadmin/account/change_password.html

@@ -15,7 +15,7 @@
                         {% include "wagtailadmin/shared/field_as_li.html" with field=field %}
                     {% endfor %}
                 </ul>
-                <input type="submit" value="{% trans 'Change Password' %}" class="button" />
+                <input type="submit" value="{% trans 'Change password' %}" class="button" />
             </form>
         {% else %}
             <p>{% trans "Your password can't be changed here. Please contact a site administrator." %}</p>

wagtail/wagtailadmin/templates/wagtailadmin/account/notification_preferences.html

@@ -1,9 +1,9 @@
 {% extends "wagtailadmin/base.html" %}
 {% load i18n %}
 
-{% block titletag %}{% trans "Notification Preferences" %}{% endblock %}
+{% block titletag %}{% trans "Notification preferences" %}{% endblock %}
 {% block content %}
-    {% trans "Notification Preferences" as prefs_str %}
+    {% trans "Notification preferences" as prefs_str %}
     {% include "wagtailadmin/shared/header.html" with title=prefs_str %}
 
     <div class="nice-padding">

wagtail/wagtailforms/templates/wagtailforms/list_submissions.html

@@ -7,7 +7,7 @@
     <thead>
         <tr>
             <th colspan="{{ data_headings|length|add:1 }}">
-                <button class="button no" id="delete-submissions" style="visibility: hidden">Delete selected submissions</button>
+                <button class="button no" id="delete-submissions" style="visibility: hidden">{% trans "Delete selected submissions" %}</button>
             </th>
         </tr>
         <tr>