npm init initializer / create-nebular-app

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [x] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**

Doing a `git clone` of this repo is not the best way to start a project. It comes with stuff related to the development of `ngx-admin`, that doesn't interest the new Nebular application.
Also, the `starter-kit` branch looks outdated compared to the `master` branch.

**Expected behavior:**

My suggestion is to transform this repo in a [npm init initializer](https://docs.npmjs.com/cli/init#description), similar to [create-react-app](https://github.com/facebook/create-react-app). IMO, that could improve the developer experience and increase the adoption of Nebular.
I understand this has a lot more components than a simple React app, but I believe it's a better experience to start with a simple app and add stuff as we need it, than to start with a big boilerplate code and remove stuff we don't need. Even the `starter-kit` branch looks bloated to me.

**Steps to reproduce:**

Compare the experience of starting a ngx-admin/Nebular app and a React app.