Changes required to replicate results in my thesis except color

This is a subset of the pull request discussed in https://github.com/ioam/topographica/pull/584. Everything related to color has been left out. Therefore, there are three changes left:
1) Extra buffer for patterns in case of motion simulations
2) Switch for input patterns (Gaussian/Images)
3) Gain control for spatial frequency
I'm not sure about the logic here -- for an 'SF' simulation, it seems to be disabling gain control if gain_control_SF is false, and it then doesn't do things like strict_tsettle that are needed for gain control.  But what if gain_control_SF==False but self.gain_control==True (i.e., SF sheets don't need gain control, but other sheets do)?   Shouldn't this be gain_control = self.gain_control or (self.gain_control_SF and 'SF' in properties)?