api: Move the API package to a dedicated subdirectory.

In order to keep all three packages (zulip, zulip_bots,
zulip_botserver) in the same repo, all package files must now
be nested one level deeper.

For instance, python-zulip-api/zulip_bots/zulip_bots/bots/, instead
of python-zulip-api/zulip_bots/bots/.

zulip/integrations/google/get-google-credentials

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+from __future__ import print_function
+import datetime
+import httplib2
+import os
+
+from oauth2client import client
+from oauth2client import tools
+from oauth2client.file import Storage
+
+try:
+    import argparse
+    flags = argparse.ArgumentParser(parents=[tools.argparser]).parse_args()
+except ImportError:
+    flags = None
+
+# If modifying these scopes, delete your previously saved credentials
+# at zulip/bots/gcal/
+# NOTE: When adding more scopes, add them after the previous one in the same field, with a space
+# seperating them.
+SCOPES = 'https://www.googleapis.com/auth/calendar.readonly'
+# This file contains the information that google uses to figure out which application is requesting
+# this client's data.
+CLIENT_SECRET_FILE = 'client_secret.json'
+APPLICATION_NAME = 'Zulip Calendar Bot'
+HOME_DIR = os.path.expanduser('~')
+
+def get_credentials():
+    # type: () -> client.Credentials
+    """Gets valid user credentials from storage.
+
+    If nothing has been stored, or if the stored credentials are invalid,
+    the OAuth2 flow is completed to obtain the new credentials.
+
+    Returns:
+        Credentials, the obtained credential.
+    """
+
+    credential_path = os.path.join(HOME_DIR,
+                                   'google-credentials.json')
+
+    store = Storage(credential_path)
+    credentials = store.get()
+    if not credentials or credentials.invalid:
+        flow = client.flow_from_clientsecrets(os.path.join(HOME_DIR, CLIENT_SECRET_FILE), SCOPES)
+        flow.user_agent = APPLICATION_NAME
+        if flags:
+            # This attempts to open an authorization page in the default web browser, and asks the user
+            # to grant the bot access to their data. If the user grants permission, the run_flow()
+            # function returns new credentials.
+            credentials = tools.run_flow(flow, store, flags)
+        else:  # Needed only for compatibility with Python 2.6
+            credentials = tools.run(flow, store)
+        print('Storing credentials to ' + credential_path)
+
+get_credentials()