Problem: Billing is always on

Solution: Make billing configurable through LIBRETIME_ENABLE_BILLING and deactivate it

This should catch all the changes needed to deactive billing in LibreTime.

* [x] only call billing when it is enabled
* [x] let super admins edit their info
* [x] dont link to billing if it is disabled

airtime_mvc/application/views/scripts/form/edit-user.phtml

@@ -1,7 +1,7 @@
 <h2><?php echo _("My Profile") ?></h2>
 <div id="current-user-container">
 
-  <?php if(Application_Model_User::getCurrentUser()->isSuperAdmin()) : ?>
+  <?php if(LIBRETIME_ENABLE_BILLING === true && Application_Model_User::getCurrentUser()->isSuperAdmin()) : ?>
     <div id="user_details_superadmin_message">
         <p class="alert alert-error">
             <?=sprintf(_("<b>Note:</b> Since you're the station owner, your account information can be edited in <a href=\"%s\">Billing Settings</a> instead."), "/billing/client");?>

airtime_mvc/application/views/scripts/form/preferences.phtml

@@ -9,7 +9,7 @@
     </div>
 
     <?php
-    if (Billing::isStationPodcastAllowed()) { ?>
+    if (LIBRETIME_ENABLE_BILLING === true && Billing::isStationPodcastAllowed()) { ?>
     <h3 class="collapsible-header" id="soundcloud-heading"><span class="arrow-icon"></span><?php echo _("SoundCloud Settings") ?></h3>
     <div class="collapsible-content" id="soundcloud-settings">
         <?php echo $this->element->getSubform('preferences_soundcloud') ?>

airtime_mvc/application/views/scripts/user/add-user.phtml

@@ -26,9 +26,11 @@
             </table>
         </div>
     </div>
+    <?php if (LIBRETIME_ENABLE_BILLING === true) { ?>
     <div class="user-data" id="user_details_superadmin_message" style="display: none; margin-top: 105px; text-align: center;">
         <?=sprintf(_("Super Admin details can be changed in your <a href=\"%s\">Billing Settings</a>."), "/billing/client");?>
     </div>
+    <?php } ?>
     <div class="user-data simple-formblock" id="user_details">
         <?php echo $this->successMessage ?>
         <fieldset class="padded">