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
```'SF' in properties``` tests whether this particular sheet is a spatial frequency sheet (channel>=2), NOT if this is a 'SF' simulation. Therefore, if you used ```gain_control = self.gain_control or (self.gain_control_SF and 'SF' in properties)``` and ```gain_control_SF==False``` and ```self.gain_control==True```, strict_tsettle and other things would be enabled for the SF sheets which do not need it, because self.gain_control==True!
When using my statement, the appropriate actions are taken depending on whether this particular sheet is a SF sheet or not. If it is a SF sheet, only ```self.gain_control_SF``` matters. And if it is a normal sheet, only ```self.gain_control``` matters.