Fixed AirMode and link-editing popup problems

AirMode and link-edit popups which resulted in dialog boxes would end up having the popup remain onscreen, interfering with the dialog display.

This fix adds two things:

1.  An argument to editor.saveRange() which causes the range to be collapsed (after saved).  This allows the "Help" dialog to temporarily collapse the selection.

2.  A new data-hide attribute for popup buttons so that certain buttons can be singled out as requiring a popup.hide() before they are executed.   The button building routines were also changed to add this in a way similar to data-value and data-event.