Can only start or end tab drag if not over close

Can only begin tabDragStart or tabDragEnd functions if overCloseLink is
false
overCloseLink flag and position new tab on close

The 3 x instances where we define closeTabLink needs the
setting/unsetting of a new var flag called overCloseLink. This is so we
can choose not to start or end a drag function.
After processing a closeTab function, set canSwitchTabs back to true in
0.1s
Finally, the newTab left position should be set according to the length
of open files, not 1 less than it and we also need to have a tab width
of 0 but compensate for the padding, so needs to be -18