Fix for some issues when the gameport is detached from the DOM

$('#foo') doesn't find elements that are detached, so e.g. the InvisibleCursor elements don't get removed when they should be. This changes it to $('#foo', parent_elem) in all instances but one. As long as the gameport is attached when GlkOte.init() is called, it can be detached and reattached later and still work reasonably well while detached.