sdk/node: add transaction tags

Afford the interface:

```js
await client.transactions.transact(builder => {
  // ...
  builder.transactionTags = tags
})

const txs = client.transactions
  .list({
    filter: `actions(snapshot.transactionTags.foo=$1)`,
    filterParams: [tags.foo],
  })
  .all()
for await (const tx of txs) {
  console.log(tx.tags)
  console.log(tx.actions[0].snapshot.transactionTags)
}
```

Closes #3638

Author: Dan Croak <dan@statusok.com>
Date: Wed May 9 15:36:37 2018 -0700
upstream:3cd4ab1f3b389171b169f956d845db2ea1895443

Author: croaky

src/api/transactions.ts

@@ -24,6 +24,9 @@ import { validate } from '../validate'
  *
  * @property {Action[]} actions
  * List of specified actions for a transaction.
+ *
+ * @property {Object} tags
+ * User-specified key-value data embedded in the transaction.
  */
 
 /**
@@ -32,6 +35,7 @@ import { validate } from '../validate'
  */
 export class TransactionBuilder {
   public actions: any[]
+  public transactionTags: any
 
   /**
    * constructor - return a new object used for constructing a transaction.
@@ -43,6 +47,13 @@ export class TransactionBuilder {
      * @type Array
      */
     this.actions = []
+
+    /**
+     * Key-value tags for the transaction.
+     * @name TransactionBuilder#transactionTags
+     * @type Object
+     */
+    this.transactionTags = null
   }
 
   /**

test/transactions.ts

@@ -75,6 +75,40 @@ describe('Transaction', () => {
       assert.deepEqual(items[0].type, 'issue')
     })
 
+    it('adds transaction tags', async () => {
+      const gold = await createFlavor('gold')
+      const alice = await createAccount('alice')
+      const tags = { foo: uuid.v4().toString() }
+
+      await client.transactions.transact(builder => {
+        builder.issue({
+          flavorId: gold.id,
+          amount: 100,
+          destinationAccountId: alice.id,
+        })
+        builder.transactionTags = tags
+      })
+
+      const txs = await testHelpers.asyncAll(client.transactions
+        .list({
+          filter: `actions(snapshot.transactionTags.foo=$1)`,
+          filterParams: [tags.foo],
+        })
+        .all())
+
+      expect(txs.length).to.equal(1)
+
+      txs.forEach(tx => {
+        assert.deepEqual(tx.tags, tags)
+        const action = tx.actions[0]
+        assert.deepEqual(action.snapshot.transactionTags, tags)
+        assert.deepEqual(action.type, 'issue')
+        assert.deepEqual(action.amount, 100)
+        assert.deepEqual(action.flavorId, gold.id)
+        assert.deepEqual(action.destinationAccountId, alice.id)
+      })
+    })
+
     it('handles large numbers', async () => {
       const gold = await createFlavor('gold')
       const alice = await createAccount('alice')