Proposal: `ng doctor` for check diff and sync to the latest project template

### Bug Report or Feature Request (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```

### Desired functionality.
After updated the CLI version, sometimes `package.json` is updated. Currently `package.json` is generated at `ng new` and never do sync to latest dependencies.

I want something like `ng doctor` to solve it. The use-case images are below:

```
$ ng doctor # listing up dependency changes
$ ng doctor --write # auto-patching on _compatible_ version (with semver ?)
```

### Mention any other details that might be useful.

從提議的 `ng doctor` 進入點和現有的 `package.json` 產生路徑開始。定義如何列出相依性差異，以及 `--write` 如何只套用 semver 相容的更新，然後為列出變更和寫入更新分別新增涵蓋測試。

由索引模型根據 Issue 內容生成。