[GUI]: Add number of restarts (and possibly other algorithm arguments) to GUI #1114

When computing equilibria, the graphical interface offers no ability to customise the behaviour of algorithms - it chooses (sensible?) defaults.

There are probably a few configuration options that would be useful to offer - even for "beginning" users. The one that comes to mind is to select the number of starting points tried, for the methods that try these; mostly these are hard-coded to 10 right now.

It could be worth looking at other algorithm parameters as well - although my own first thought is that most of them could comfortably be set at sensible defaults and leave it at that (as they are now).