06 new ignore owerlap method v27

Hello!
I try to do some refactoring code. There I combine the "Ignore conflict" and "force overlap" options into single one. Selector control with tree states is used. Now status is "beta":
For "add session" it working fine (except bug that I was early report)
For "add single slot" currently cannot delete overlapped slot - 
$cslot = $this->$scheduler->get_slot($conflict->id);
-raise error
Also need correct strings and help messages, etc.
If you will approve this idea in general - I will continue looking for an error solution