TVB-2698: Fixed launching simulations with stimuli

Created by: VinczeRobert

I fixed simulation launching with both kinds of stimuli. I went with the assumption that if you have a surface chosen, then only surface stimuli can be chosen, otherwise only region stimuli, based on the code in SimulatorStimulusFragment.

I suggest to merge TVB-2651 first, so I can make a rebase and test each visualizer with these type of surfaces to make sure they are okay.