used urllib2 instead of requests

[zonito]

requests is not working with other applications such as google appengine.

ref: http://stackoverflow.com/questions/9604799/can-python-requests-library-be-used-on-google-app-engine/28544823#28544823

Suggest any change in code required.

Note: Also fixed some pylints.

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[geeknam]

I'm pretty sure you can use requests on GAE. It was a conscious decision to use requests library. Requests is a widely use package and it simplifies lots of things. You can use the old pypi package of python-gcm if you want urllib2 support.