MDL-21137 MNet: UI to choose peer theme replaced with simple selector

There is no need to have whole featured theme selector with previews
etc here. Following the same form element as they have in Mahara, the
theme can now be selected for a given peer at 'Review host details' tab.
I have also noticed that force_theme and theme columns are redundant at
the moment. Keeping them both for future improvements, though.

admin/mnet/peer_forms.php

@@ -86,6 +86,13 @@ class mnet_review_host_form extends moodleform {
 
         $mform->addElement('text', 'wwwroot', get_string('hostname', 'mnet'));
         $mform->setType('wwwroot', PARAM_URL);
+
+        $themes = array('' => get_string('forceno'));
+        foreach (array_keys(get_plugin_list('theme')) as $themename) {
+            $themes[$themename] = get_string('pluginname', 'theme_'.$themename);
+        }
+        $mform->addElement('select', 'theme', get_string('forcetheme'), $themes);
+
         $mform->addElement('textarea', 'public_key', get_string('publickey', 'mnet'), array('rows' => 17, 'cols' => 100, 'class' => 'smalltext'));
         $mform->setType('public_key', PARAM_PEM);