Replace state transition helper functions with optimized versions.

### What is wrong?

In https://github.com/ethereum/trinity/pull/1918, we copied https://github.com/protolambda/eth2fastspec into our repo and made the minimal changes required for compatibility. A major improvement in code quality would be to replace the existing helper functions with their optimized versions.

### How can it be fixed

- [ ] replace existing helper functions with optimized versions
- [x] raise `ValidationErrors` instead of `AssertionErrors` when validation fails ethereum/trinity#1977
- [x] parameterize config values, instead of hardcoding Altona values https://github.com/ethereum/trinity/pull/1967
- [ ] ensure that spec tests are running on optimized helper functions