Finish unimplemented preconditions

[mitschabaude]

• Closes Finish unimplemented preconditions #240
• Implements all remaining preconditions, except two that are blocked by protocol work.
  • Ones that are still missing: network.epochData.seed is not checked on the protocol side yet; account.provedState is not available via graphql yet
• Expose most of the account fields for accounts in the local ledger to JS, so we can use them for account preconditions
• Add JS equivalents of encoding functions for various hashes: receipt chain hash, ledger hash etc. These are implemented as follows:
  • The Field that represents the hash is serialized to bytes in a way that mirrors the bin_prot serialization on the OCaml side (which is pretty straightforward -- just the bytes of the Field plus an optional version number at the beginning)
  • The conversion from bytes to a base58 string is done by using the base58_check lib from OCaml. "Version bytes" for different types which are expected by this lib are also imported from OCaml
• Move getDefaultTokenId and base58 encoders for token ids to a common namespace, TokenId, which is used internally. Export that namespace to the outside by putting it on Token.Id, i.e. as sub-namespace on the existing Token class

[Trivo25]

A general namespace for base58 encoders is a great improvement!

[ymekuria]

LGTM!