fix(@angular/cli); show only changed chunks on build

For projects with a lot of lazy modules the rebuild messages can easily fill the whole console window.

This PR shows only chunks that changed instead of showing all chunks.

Before:
```
$ ng serve
** NG Live Development Server is listening on localhost:4200, open your browser on http://localhost:4200/ **
Date: 2017-12-14T14:56:13.707Z
Hash: 7490b2942c48ffcf0f0f
Time: 7317ms
chunk {inline} inline.bundle.js (inline) 5.79 kB [entry] [rendered]
chunk {main} main.bundle.js (main) 725 kB [initial] [rendered]
chunk {polyfills} polyfills.bundle.js (polyfills) 577 kB [initial] [rendered]
chunk {styles} styles.bundle.js (styles) 35 kB [initial] [rendered]
chunk {vendor} vendor.bundle.js (vendor) 6.45 MB [initial] [rendered]

webpack: Compiled successfully.
webpack: Compiling...
Date: 2017-12-14T14:56:17.054Z
Hash: dbb03cc0994e8bf69e76
Time: 310ms
chunk {inline} inline.bundle.js (inline) 5.79 kB [entry]
chunk {main} main.bundle.js (main) 725 kB [initial] [rendered]
chunk {polyfills} polyfills.bundle.js (polyfills) 577 kB [initial]
chunk {styles} styles.bundle.js (styles) 35 kB [initial]
chunk {vendor} vendor.bundle.js (vendor) 6.45 MB [initial]

webpack: Compiled successfully.
webpack: Compiling...
Date: 2017-12-14T14:56:20.290Z
Hash: fe53cbcd529dd2508cfc
Time: 267ms
chunk {inline} inline.bundle.js (inline) 5.79 kB [entry]
chunk {main} main.bundle.js (main) 725 kB [initial]
chunk {polyfills} polyfills.bundle.js (polyfills) 577 kB [initial] [rendered]
chunk {styles} styles.bundle.js (styles) 35 kB [initial]
chunk {vendor} vendor.bundle.js (vendor) 6.45 MB [initial]

webpack: Compiled successfully.
```

After:
```
$ ng serve
** NG Live Development Server is listening on localhost:4200, open your browser on http://localhost:4200/ **
Date: 2017-12-14T14:53:40.216Z
Hash: 44065f5ec5c4c8cf884a
Time: 7312ms
chunk {inline} inline.bundle.js (inline) 5.79 kB [entry] [rendered]
chunk {main} main.bundle.js (main) 724 kB [initial] [rendered]
chunk {polyfills} polyfills.bundle.js (polyfills) 576 kB [initial] [rendered]
chunk {styles} styles.bundle.js (styles) 35 kB [initial] [rendered]
chunk {vendor} vendor.bundle.js (vendor) 6.45 MB [initial] [rendered]

webpack: Compiled successfully.
webpack: Compiling...
Date: 2017-12-14T14:53:42.089Z
Hash: 492a7350b12ec1557b61
Time: 241ms
chunk {main} main.bundle.js (main) 725 kB [initial] [rendered]
4 unchanged chunks

webpack: Compiled successfully.
webpack: Compiling...
Date: 2017-12-14T14:53:49.762Z
Hash: 7490b2942c48ffcf0f0f
Time: 296ms
chunk {polyfills} polyfills.bundle.js (polyfills) 577 kB [initial] [rendered]
4 unchanged chunks

webpack: Compiled successfully.
```

Fix #8621

packages/@angular/cli/utilities/stats.ts

@@ -26,11 +26,9 @@ export function statsToString(json: any, statsConfig: any) {
   const g = (x: string) => colors ? bold(green(x)) : x;
   const y = (x: string) => colors ? bold(yellow(x)) : x;
 
-  return rs(stripIndents`
-    Date: ${w(new Date().toISOString())}
-    Hash: ${w(json.hash)}
-    Time: ${w('' + json.time)}ms
-    ${json.chunks.map((chunk: any) => {
+  const changedChunksStats = json.chunks
+    .filter((chunk: any) => chunk.rendered)
+    .map((chunk: any) => {
       const asset = json.assets.filter((x: any) => x.name == chunk.files[0])[0];
       const size = asset ? ` ${_formatSize(asset.size)}` : '';
       const files = chunk.files.join(', ');
@@ -41,7 +39,18 @@ export function statsToString(json: any, statsConfig: any) {
         .join('');
 
       return `chunk {${y(chunk.id)}} ${g(files)}${names}${size} ${initial}${flags}`;
-    }).join('\n')}
+    }).join('\n');
+
+  const unchangedChunkNumber = json.chunks.filter((chunk: any) => !chunk.rendered).length;
+  const unchangedChunksMessage = unchangedChunkNumber > 0
+    ? `${unchangedChunkNumber} unchanged chunks`
+    : '';
+
+  return rs(stripIndents`
+    Date: ${w(new Date().toISOString())}
+    Hash: ${w(json.hash)}
+    Time: ${w('' + json.time)}ms
+    ${changedChunksStats ? changedChunksStats + '\n' : ''}${unchangedChunksMessage}
     `);
 }