Add (and use) functions to the datamodel to determine plotting parameters

[albireox]

Kyle is going to provide functions that, based on an array, will return the optimal plotting limits for that array. There will be different functions for different types of properties. Each MapsProperty needs to gain an attribute that contains the function to use to define the plot limits. Map should then gain a method that returns the limits for itself. The tools and the web need to be updated to use that methods and the appropriate limits.

[bretthandrews]

I've incorporated this into my map plotting changes, though it could use some refinement because it currently only distinguishes between vel, sigma, and other.

[havok2063]

Can we close this issue?