Added function to compute prior assuming uniform (uninformative) priors for all parameters. If this is not the case, the function can be overwridden by the user.
Added method to get the save directory.
The transparency in either the radial or z direction in the disk_concentric_ring model can be disabled by zetting alpha or beta outside of bounds. We may want to subclass disk_concentric_rings instead of doing this to make the UI function as expected.
Output directory can now be set via. command line. Multiple instances of SIMTOI *should* be able to execute at the same time, providing minimizers don't share memory space.