docs: Added additional documentation for specifying OAuth scopes.

- from: /guide/google/gcm/server-javadoc/...

  to: /reference/com/google/android/gcm/server/package-summary.html

- from: /google/play-services/auth.html

  to: /google/auth/http-auth.html

- from: /guide/google/play/services.html

  to: /google/play-services/index.html

"{@docRoot}reference/com/google/android/gms/auth/GoogleAuthUtil.html#getToken(android.content.Context,%20java.lang.String,%20java.lang.String)">

{@code GoogleAuthUtil.getToken()}</a>, you must provide the app {@link android.content.Context},

the account name retrieved from the account picker, and the scope for your auth

token request. The above sample code (and the attached sample) defines these arguments with

class members that the host activity passes to

the {@link android.os.AsyncTask} class constructor.</p>

token request. The above sample code (and the attached sample) defines these

arguments with class members that the host activity passes to the {@link android.os.AsyncTask} class constructor. For more information about setting the scope, see

the <a href="#SpecifyingScopes">Specifying Scopes</a> section below. </p>

<p class="note"><strong>Note:</strong>

As shown by the {@code fetchToken()} method above, you must handle

"{@docRoot}reference/com/google/android/gms/auth/GoogleAuthUtil.html#getToken(android.content.Context,%20java.lang.String,%20java.lang.String)">

{@code GoogleAuthUtil.getToken()}</a>.</p>

<h3 id="SpecifyingScopes">Specifying scopes</h3>

<p>The scope string is used to specify which Google services can be accessed by

  an app using the requested auth token. An auth token can be associated with

  multiple scopes.</p>

<p>When specifying the scopes in your auth token request, prefix the

  scope string with {@code "oauth2:"} followed by a list of one or more OAuth scope

  values. Use a space to separate each scope value in the list. To see a list of

  valid OAuth scope values for Google services, browse

  the <a href="https://developers.google.com/oauthplayground/"

  class="external-link">OAuth 2.0 Playground</a>.</p>

<p class="note"><strong>Tip:</strong> Specify {@code "oauth2:&lt;scope&gt;"}

  for a single scope. Specify

  {@code "oauth2:<scope1> <scope2> <scopeN>"} for multiple

  scopes (using a space to separate each scope).</p>

<p>For example, to access the Google Books API, the scope is

  {@code "oauth2:https://www.googleapis.com/auth/books"}. To add an additional

  scope, say for Google+ login, your code might look like this:</p>

<pre>

private final static String BOOKS_API_SCOPE

        = "https://www.googleapis.com/auth/books";

private fina; static String GPLUS_SCOPE

        = "https://www.googleapis.com/auth/plus.login";

private final static String mScopes

        = "oauth2:" + BOOKS_API_SCOPE + " " + GPLUS_SCOPE;

String token = GoogleAuthUtil.getToken(mActivity, mEmail, mScopes);

</pre>

<h2 id="HandleExceptions">Handle Exceptions</h2>