Sol Type re-factoring

[prestwich]

This creates a new trait that distinguishes SolType from SolDataType

motivation:

• structs and primtives can be struct properties, but errors and events cannot
• capture above relationship in type system
• do not implement eip712 for errors or events (As it is always incorrect behavior)
• do not implement encodePacked for errors or events (same reason)

solution:

• Introduce a new trait which describes data types and includes 712 and encodePacked
• this trait is implemented for structs, udts, primitives, compound types

new type system

• SolType
  • SolDataType
    • primitive types
    • UDTs
    • SolStruct
  • SolError
  • SolEvent (TODO)
  • SolCallArgs (TODO)