Add a GUI field to enable istgt in multithreaded mode

Defaults to off.

Ticket:	#4935
(cherry picked from commit a4018bd8a74cdef2ca234ce89b35a1c3757ddfe5)
Use -m 2 for istgt in case multithread is enabled

Ticket:	#4935
(cherry picked from commit 9b0916b64406359138e57a2cfb7707e026e48e6a)