openSessionList() now closes any already-open overlay itself before
rendering, so a double-tap on the stack bar (which has no lock) can no
longer stack two session lists with duplicate handlers. The onMove/
onRemove callbacks no longer need their own closeOverlays() call since
openSessionList() does it unconditionally now.
onEndSession no longer calls syncView() after clearSession(), which
was writing the freshly emptied session straight back into storage and
undoing the clear. It now only refreshes the visible stacks, so ending
a session actually leaves nothing saved, while a subsequent scan still
saves normally via syncView().
vchuser
b06b3abfd5