This PR adds the global scripts functionality. It will allow users to designate javascript files to be loaded as if they were in a scripts tag in index.html. Global styles will be bundled in styles.bundle.js and global scripts will be in scripts.bundle.js, both loaded before main.bundle.js.

It also changes apps[0].styles to be an array in order to match the new apps[0].scripts and better allow loading scripts and styles together.

angular-cli.json :

{
  // ...
  "apps": [
    {
      // ...
      "styles": [
        "styles.css"
      ],
      "scripts": [ ],
      // ...
    }
  ],
  // ...
}

Closes #1717

Functionality description in README:

Global Library Installation

Some javascript libraries need to be added to the global scope, and loaded as if
they were in a script tag. We can do this using the apps[0].scripts and
apps[0].styles properties of angular-cli.json.

As an example, to use Boostrap 4 this is
what you need to do:

First install Bootstrap from npm:

npm install bootstrap@next

Then add the needed script files to to apps[0].scripts.

"scripts": [
  "../node_modules/jquery/dist/jquery.js",
  "../node_modules/tether/dist/js/tether.js",
  "../node_modules/bootstrap/dist/js/bootstrap.js"
],

Finally add the Bootstrap CSS to the apps[0].styles array:

"styles": [
  "styles.css",
  "../node_modules/bootstrap/dist/css/bootstrap.css"
],

Restart ng serve if you're running it, and Bootstrap 4 should be working on
your app.