filebrowser: Make the "Open terminal here" command work again

Add a gsettings key to set the terminal used for the command in the menu. By
default this is set to 'x-terminal-emulator' but it can be easily overridden
by packagers or changed by users who choose to.

plugins/filebrowser/org.x.editor.plugins.filebrowser.gschema.xml.in

@@ -16,6 +16,11 @@
       <summary>File Browser Filter Pattern</summary>
       <description>The filter pattern to filter the file browser with. This filter works on top of the filter_mode.</description>
     </key>
+    <key name="terminal-command" type="s">
+      <default>'x-terminal-emulator'</default>
+      <summary>Terminal Command</summary>
+      <description>The terminal command when using the "Open terminal here" command.</description>
+    </key>
     <child name="on-load" schema="org.x.editor.plugins.filebrowser.on-load"/>
   </schema>
   <schema id="org.x.editor.plugins.filebrowser.on-load" path="/org/x/editor/plugins/filebrowser/on-load/">

plugins/filebrowser/xed-file-browser-plugin.c

@@ -337,13 +337,6 @@ on_action_set_active_root (GtkAction            *action,
     set_root_from_doc (plugin, xed_window_get_active_document (XED_WINDOW (plugin->priv->window)));
 }
 
-static gchar *
-get_terminal (XedFileBrowserPlugin *plugin)
-{
-    // TODO : Identify the DE, find the preferred terminal application (xterminal shouldn't be hardcoded here, it should be set as default in the DE prefs)
-    return g_strdup ("xterminal");
-}
-
 static void
 on_action_open_terminal (GtkAction            *action,
                          XedFileBrowserPlugin *plugin)
@@ -369,8 +362,7 @@ on_action_open_terminal (GtkAction            *action,
         gchar *local;
         gchar *argv[2];
 
-        terminal = get_terminal (plugin);
-
+        terminal = g_settings_get_string (priv->settings, "terminal-command");
         local = g_file_get_path (file);
 
         argv[0] = terminal;