add getInterchain: trace a transaction/block to validator blocks + interchain anchors

New transaction.getInterchain and block.getInterchain call the prime-node
/api/v1/{transaction,block}/{id}/interchain endpoints, returning an
InterchainTrace { blockId, validatorBlocks, interchainTransactions }. Adds
VerificationBlock / InterchainTransaction / InterchainTrace interfaces and
method-existence assertions.

tests/sdk.test.ts

@@ -47,6 +47,7 @@ describe('DragonchainSDK', () => {
       expect(typeof sdk.transaction.create).toBe('function');
       expect(typeof sdk.transaction.createBulk).toBe('function');
       expect(typeof sdk.transaction.get).toBe('function');
+      expect(typeof sdk.transaction.getInterchain).toBe('function');
       expect(typeof sdk.transaction.list).toBe('function');
     });
 
@@ -68,6 +69,7 @@ describe('DragonchainSDK', () => {
 
     it('should have block module with correct methods', () => {
       expect(typeof sdk.block.get).toBe('function');
+      expect(typeof sdk.block.getInterchain).toBe('function');
     });
 
     it('should have system module with correct methods', () => {