Bug 1046564: Should display normal priority message of STK_CMD_DISPLAY_TEXT command while device is Settings

To show the normal priority message of STK_CMD_DISPLAY_TEXT command when the device is both HomeScreen and Settings. 
NIT: instead use the origin URL directly, it's better to avoid domain dependency doing this:

    var settingsOrigin = document.location.protocol + '//' +
      document.location.host.replace('system', 'settings');

and compare with this variable. The same as here [1]

[1] https://github.com/mozilla-b2g/gaia/blob/master/apps/system/js/icc_worker.js#L322