Reorganize types and add consistency tests

[wemeetagain]

Resolves #83 and the first part of #84

The added tests compare our interface definitions against our variable definitions to ensure that:

1. For every interface, a "runtime type" variable of the same name exists
2. For every field (in every interface), the same field name and type is defined in the corresponding "runtime type" variable's field

As part of this, the types have been reorganized:

• to be in dependency order (eg: if interface A relies on interface B, A has been moved before interface B)
• primitive types (eg: bytes, uint64, etc) have been moved into their own file
• attestation types have been moved into their own file

Also, all var runtime types have been turned into consts.

[GregTheGreek]

I really like this, also much needed refactor 👍