2d neighbors

[streeve]

Enable 2d neighbor construction and iteration. Dimension extracted from particle data in creation functions with default 3d template dimension in classes for backwards compatibility

Other notes:

• ArborX does not support 2d as far as I can tell
• New VerletList creation functions
• Adds new discriminator for LinkedCellList

Part of #490

[streeve]

Ok @lebuller this is ready for review. Looking into a good way to do the ArborX lists and planning to add 2d tests, but otherwise ready.

Also probably good to move those last two commits to a separate PR if you agree

[aprokop]

Ok @lebuller this is ready for review. Looking into a good way to do the ArborX lists and planning to add 2d tests, but otherwise ready.

What do you mean by "good way to do the ArborX lists"?

[streeve]

What do you mean by "good way to do the ArborX lists"?

Haven't tried yet, but I'd like to extract the dimension from the positions directly. Which would be nice across all cases honestly

[lebuller]

Looks mostly good to me, we should probably add tests of the 2D list capabilities as well which don't seem to be included

[streeve]

@lebuller ready for another review - the new creation functions extract the dimension from the particles directly. You could still explicitly construct an object if those don't match if necessary