Convenience function for multi-panel map plots

[bretthandrews]

Add plotting function for Maps that implements something similar to the example code given in the Multi-panel Plot section of the plotting tutorial.

• [ ] By default, show the three default maps (stellar vel, Ha flux, D4000).
• [ ] Optionally take in a map grouping keyword to show a pre-defined set of maps (e.g., "kinematics" would correspond to stellar_vel and stellar_sigma).
• [ ] Optionally accept a list of maps to display.