Implement Error constricting functions

[calebbourg]

Implement methods for constructing error structs for the various types of errors we define.

Current Usage:

  // Lines 64-67, 88-93, 167-170, 186-189
  Error {
      source: None,
      error_kind: DomainErrorKind::Internal(InternalErrorKind::Other(
          "Some error message".to_string(),
      )),
  }

Proposed Usage

Error::internal("At least one recipient is required")

Proposed in comment here