Implement visibility flag in pattern metadata

[CSergienko]

We need to distinguish between those variations which are demonstrative (for the mote explorer) and those which are purely functional. To this end, we need to implement a flag in the metadata.yaml which would allow us to toggle the visibility of the entire pattern, or a single variation.

I suggest treating this visibility flag as False by default, which will force the maintainer of the pattern library to more carefully consider what ends up in the interface.