Add bed gradient view with various defect options

[sjasonsmith]

This expands the bed implementation of the simulator in two key ways:

1. Add a gradient option, which visualizes the Z height of the bed at various locations. As part of this the bed visualization was expanded into a larger number of triangles so that each vertex contains Z and color information. \ This change will become useful with the default planar bed when expanding the simulator to better model multi-Z configurations, where visualizing the position of the plane will help verify G34 functionality.

2. Add various bed shape options, which will overlap geometric patterns on top of the default planar bed. This allows for testing of bed leveling algorithms with more than an uneven plane.

[sjasonsmith]

Sample of the various patterns displayed on the bed:

[p3p]

After days of significant testing, okay 30mins .. mostly spent configuring Marlin for UBL I can confirm this does appear to do what you said it does.