Create a class to represent a dust particle in a plasma

[namurphy]

Dust is common in many plasmas such as the interstellar medium (ISM). (Yay space dust!) We should have a means of representing dust particles somewhere in plasmapy.particles, perhaps called DustParticle.

Dust particles have some basic attributes like mass and charge. There will be more complicated attributes like composition, which I'm not sure how to describe. There will likely need to be subclasses such as SphericalDustParticle and EllipticalDustParticle. I don't know if this should be a subclass of CustomParticle (#447, #755).

We should talk with dusty plasma physicists to get their thoughts on what should be included in DustParticle and how we describe it.

[namurphy]

We should talk with dusty plasma physicists to get their thoughts on what should be included in DustParticle and how we describe it.

To clarify, we should talk with (dusty plasma) physicists, not dusty (plasma physicists). Then again, maybe we could find and ask a dusty [(dusty plasma) physicist].