@nativescript/webpack rewrite

The rewrite allows us to simplify things, and introduce some breaking changes. Listing them here, so we can keep track of them - will be in the merge commit, and the release notes once we are ready.

BREAKING CHANGES:

• package.json main should now use a relative path to the package.json instead of the app directory

  For example (given we have a src directory where our app is):

  "main": "app.js" becomes "main": "src/app.js" OR "main": "src/app.ts" (whether using JS or TS)

  This simplifies things, and will allow ctrl/cmd + clicking on the filename in some editors.

• postinstall scripts have been removed.

  The configuration will not need to change in the user projects between updates.

  For existing projects we will provide an easy upgrade path, through ns migrate and a binary in the package.

  For new projects ns create should create the config file by invoking a binary in the package.

• removed resolutions for short imports - use full imports instead.

  For example:

  import http from 'http'
  // becomes
  import { http } from '@nativescript/core'