housekeep: TU rename - code changes

Renaming of symbols. Functions, variables, values, DB values, etc.
Basically everything that is not user-facing.

This only covers "Trusted User" things:
tests, comments, etc. will covered in a following commit.

templates/partials/archdev-navbar.html

@@ -37,7 +37,7 @@
             </li>
 
             {# Only CRED_TU_LIST_VOTES privileged users see Trusted User #}
-            {% if request.user.has_credential(creds.TU_LIST_VOTES) %}
+            {% if request.user.has_credential(creds.PM_LIST_VOTES) %}
                 <li>
                     <a href="/tu">{% trans %}Trusted User{% endtrans %}</a>
                 </li>

templates/partials/packages/search_actions.html

@@ -4,7 +4,7 @@
             <option value="unflag">{{ "Unflag Out-of-date" | tr }}</option>
             <option value="adopt">{{ "Adopt Packages" | tr }}</option>
             <option value="disown">{{ "Disown Packages" | tr }}</option>
-        {% if request.user.is_trusted_user() or request.user.is_developer() %}
+        {% if request.user.is_package_maintainer() or request.user.is_developer() %}
             <option value="delete">{{ "Delete Packages" | tr }}</option>
         {% endif %}
         <option value="notify">{{ "Notify" | tr }}</option>

templates/partials/packages/statistics.html

@@ -44,7 +44,7 @@
             <td class="stat-desc">
                 {{ "Trusted Users" | tr }}
             </td>
-            <td>{{ trusted_user_count }}</td>
+            <td>{{ package_maintainer_count }}</td>
         </tr>
     </table>
 </div>

templates/partials/tu/proposals.html

@@ -1,7 +1,7 @@
 <div class="box">
     <h2>{% trans %}{{ title }}{% endtrans %}</h2>
 
-    {% if title == "Current Votes" and request.user.has_credential(creds.TU_ADD_VOTE) %}
+    {% if title == "Current Votes" and request.user.has_credential(creds.PM_ADD_VOTE) %}
         <ul class="admin-actions">
             <li>
                 <a href="/addvote">