Add a default particle filter for Enzo

[yt-fido]

Originally reported by: Matt Turk (Bitbucket: MatthewTurk, GitHub: MatthewTurk)

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Right now (as pointed out by @rthompson ) particle filters for Star particles from "old" Enzo aren't set up. We may want to do this, so that they show up in particle types. For reference:

#define PARTICLE_TYPE_GAS            0
#define PARTICLE_TYPE_DARK_MATTER    1
#define PARTICLE_TYPE_STAR           2
#define PARTICLE_TYPE_TRACER         3
#define PARTICLE_TYPE_MUST_REFINE    4
#define PARTICLE_TYPE_SINGLE_STAR    5
#define PARTICLE_TYPE_BLACK_HOLE     6
#define PARTICLE_TYPE_CLUSTER        7
#define PARTICLE_TYPE_MBH            8
#define PARTICLE_TYPE_COLOR_STAR     9
#define PARTICLE_TYPE_SIMPLE_SOURCE 10

This would likely come in around the time that default particle unions are set up.

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• Bitbucket: https://bitbucket.org/yt_analysis/yt/issue/1193