API: Add types for ledgercore.StateDelta.

[winder]

• Add types for LedgerStateDelta.
• Add generated types for new status fields.
• Add strict encoder, currently only used by tests.
• Fix bug where encoding errors were ignored.
• Disable block header response test which has never worked, opened issue: Cucumber BLOCK test unit.stateproof.responses.msgp does not work properly. #469
• Map keys are encoded in an unexpected way leading to a type mismatch in the test code, opened issue: Unexpected encoding with interface{} key using Canonical and MapKeyAsString. ugorji/go#390
• Disable @unit.stateproof.responses.msgp due to the above two issues.
• Created a "skipped" test in json_encode.go as another reminder (in addition to the above issues).

[shiqizng]

please add these definitions, too

const (
	// TealBytesType represents the type of a byte slice in a TEAL program
	TealBytesType TealType = 1

	// TealUintType represents the type of a uint in a TEAL program
	TealUintType TealType = 2
)
// Status is the delegation status of an account's MicroAlgos
type Status byte
const (
Offline Status = iota
Online
NotParticipating
)