Allow showing or hiding a limited set of twisters

[nhthn]

Options I should have for a regular polytwister:

• Show all twisters.
• Show a single twister.
• Show a pair of adjacent twisters.

Options I should have for a non-regular uniform polytwister:

• Show all twisters.
• Show orbit 1 only.
• Show orbit 2 only.
• Show a single twister from orbit 1.
• Show a single twister from orbit 2.
• Show a pair of adjacent twisters, necessarily one per orbit.
• Show orbit 1 and a single twister from orbit 2.
• Show orbit 2 and a single twister from orbit 1.

For the best UI, showing individual twisters would be best if the user could select the twister with the mouse, which would require JS-side raycasting.