Added curtain pattern

[lexbailey]

Hey. Dan from York Hackspace, The cube is awesome and I wanted to make a pattern for it. I have made "curtain". It's mostly just a big look up table and the colours aren't great but the animation looks okay. I might try and make the colour look better.

[pbrook]

Looks like it should be fairly simple to generate that pattern algorithmically?
Walk along a diagonal (i.e. incrementing both x any y), clamping actual coordinates to the limits of the cube.

I suggest using numpy arrays rather than building your own with nested lists (colormatrix in particular)

For sparse patterns like this it's more efficient to use cube.clear, and just populate the colored pixels.

The name in the comment at the top of the file doesn't match that used elsewhere :-)

self.filling_color looks like a copy/paste remnant.