Add vector mode for batch running simulations

[andermi]

Implement a mode switch matrix_mode: False for use in the sim_params_yaml file for batch running that would use a vector mode instead of a large test matrix using meshgrid. The solution would have to handle parameter arrays of different lengths in some way (error out or pad with a value). Simplest thing might be to require arrays of parameters to be the same length and all other parameters to be a scalar (which would be padded with that scalar value to match the length of the arrays of parameters).