Google Authentication

Added google authentication.
Made the server independent of working directory.

cloudCS can now run either in multiuser mode that requires authentication, or in standalone desktop mode.
````
$ bin/cswebgui.py -h
usage: cswebgui.py [-h] [--port PORT] [--headless] [--multiuser]

Start Circuitscape Cloud

optional arguments:
  -h, --help   show this help message and exit
  --port PORT
  --headless
  --multiuser
````