Entity-attribute-value stuff

**Resolves issue #200.**
**Contains destructive South migrations.**

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At the moment, almost everything works. Here are the remaining problems:

- There are validator tests but no model-specific EAV tests.
    - (At this point I don't really care. Let's just get this merged.)

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- [x] Tests pass
- [x] Maintain migration works
- [x] EAV form fields work correctly
- [x] Autocomplete works correctly
- [x] DHCP builds still work