sessionMode: Add 'input-method' to status icons in user mode

We now drop all status icons that are not explicitly enabled, which
breaks the ibus icon. Add it to the list of allowed icons until we
merge it with the keyboard one.

https://bugzilla.gnome.org/show_bug.cgi?id=677058

js/ui/sessionMode.js

@@ -67,7 +67,7 @@ const _modes = {
               extraStylesheet: null,
               statusArea: {
                   order: [
-                      'a11y', 'keyboard', 'volume', 'bluetooth',
+                      'input-method', 'a11y', 'keyboard', 'volume', 'bluetooth',
                       'network', 'battery', 'userMenu'
                   ],
                   implementation: STANDARD_STATUS_AREA_SHELL_IMPLEMENTATION