feat(@embark/core): Support directives in ENS config

Support directives in ENS configurations, such that subdomains can be registered to addresses of deployed tokens.

The following directives are supported:
```
"register": {
      "rootDomain": "embark.eth",
      "subdomains": {
        "status": "0x4a17f35f0a9927fb4141aa91cbbc72c1b31598de",
        "mytoken": "$MyToken",
        "MyToken2": "$MyToken2"
      }
    }
```

Add unit test for these directives.

src/lib/modules/ens/index.js

@@ -223,6 +223,7 @@ class ENS {
     this.events.request("blockchain:defaultAccount:get", (defaultAccount) => {
       async.each(Object.keys(this.registration.subdomains), (subDomainName, eachCb) => {
         const address = this.registration.subdomains[subDomainName];
+        const directivesRegExp = new RegExp(/\$(\w+\[?\d?\]?)/g);
         this.ensResolve(`${subDomainName}.${this.registration.rootDomain}`, (error, currentAddress) => {
           if (currentAddress && currentAddress.toLowerCase() === address.toLowerCase()) {
             return eachCb();
@@ -233,14 +234,30 @@ class ENS {
             return eachCb(error);
           }
 
+          const directives = directivesRegExp.exec(address);
+          if (directives && directives.length) {
+            this.embark.registerActionForEvent("contracts:deploy:afterAll", async (deployActionCb) => {
+              this.events.request("contracts:contract", directives[1], (contract) => {
+                if(!contract) return deployActionCb(); // if the contract is not registered in the config, it will be undefined here
+                const reverseNode = utils.soliditySha3(contract.deployedAddress.toLowerCase().substr(2) + reverseAddrSuffix);
+                this.registerSubDomain(defaultAccount, subDomainName, reverseNode, contract.deployedAddress, secureSend, deployActionCb);
+              });
+            });
+            return eachCb();
+          }
+
           const reverseNode = utils.soliditySha3(address.toLowerCase().substr(2) + reverseAddrSuffix);
-          ENSFunctions.registerSubDomain(this.ensContract, this.registrarContract, this.resolverContract, defaultAccount,
+          this.registerSubDomain(defaultAccount, subDomainName, reverseNode, address, secureSend, eachCb);
-            subDomainName, this.registration.rootDomain, reverseNode, address, this.logger, secureSend, eachCb);
         });
       }, cb);
     });
   }
 
+  registerSubDomain(defaultAccount, subDomainName, reverseNode, address, secureSend, cb) {
+    ENSFunctions.registerSubDomain(this.ensContract, this.registrarContract, this.resolverContract, defaultAccount,
+      subDomainName, this.registration.rootDomain, reverseNode, address, this.logger, secureSend, cb);
+  }
+
   createResolverContract(config, callback) {
     this.events.request("blockchain:contract:create", {
       abi: config.resolverAbi,

test_apps/test_app/config/namesystem.json

@@ -8,7 +8,9 @@
     "register": {
       "rootDomain": "embark.eth",
       "subdomains": {
-        "status": "0x4a17f35f0a9927fb4141aa91cbbc72c1b31598de"
+        "status": "0x4a17f35f0a9927fb4141aa91cbbc72c1b31598de",
+        "mytoken": "$MyToken",
+        "MyToken2": "$MyToken2"
       }
     }
   }

test_apps/test_app/test/namesystem_spec.js

@@ -0,0 +1,38 @@
+/*global describe, it, web3, config*/
+const assert = require('assert');
+const MyToken = require('Embark/contracts/MyToken');
+const MyToken2 = require('Embark/contracts/MyToken2');
+const EmbarkJS = require('Embark/EmbarkJS');
+
+config({
+  contracts: {
+    "Token": {
+      deploy: false,
+      args: [1000]
+    },
+    "MyToken": {
+      instanceOf: "Token"
+    },
+    "MyToken2": {
+      instanceOf: "Token",
+      args: [2000]
+    }
+  }
+});
+
+describe("ENS functions", function() {
+  it('should allow directives in ENS subdomains', async function() {
+    const myTokenAddress = await EmbarkJS.Names.resolve('mytoken.embark.eth');
+    assert.strictEqual(MyToken.options.address, myTokenAddress);
+    
+    const myToken2Address = await EmbarkJS.Names.resolve('MyToken2.embark.eth');
+    assert.strictEqual(MyToken2.options.address, myToken2Address);
+    
+    const myTokenName = await EmbarkJS.Names.lookup(MyToken.options.address.toLowerCase());
+    assert.strictEqual(myTokenName, 'mytoken.embark.eth');
+    
+    const myToken2Name = await EmbarkJS.Names.lookup(MyToken2.options.address.toLowerCase());
+    assert.strictEqual(myToken2Name, 'MyToken2.embark.eth');
+  });
+});
+