Blender Git Loki

GP "Add Monkey" - Check if there's an existing palette/colors with the required names before adding new ones

Now, when adding a Monkey primitive to the same GP object more than once,
you won't get two separate palettes (with two separate sets of colors)
created - one for each instance. Instead, the second (and subsequent)
copies will all use the initial/existing palette instance.

Note: For layers, we still just create new ones, as it makes it easier to
isolate the instances.