Singular matrix error

[celiasmith]

When you try to create a population with a lot of dimensions and not very many neurons, it gives an error that the matrix is singular. This is kind of a good idea, as people might not realize what they are doing... however, rather than throwing an error and kicking you out, it should present you with an 'override' button. Assuming, if someone pushes that, they have a good reason to.

There are reasons to: if I want to run a 500D population in direct mode, then i should be able to create it with just 1 neuron. It gets annoying to have the system force you to create populations with thousands of neurons when you don't plan on using them.