Added support of custom RSS services compatible with Google Reader API

Hello Sun Zheng,
In the process of enabling an API compatible with Google Reader in the [FreshRSS project](http://freshrss.org) (fully Open Source), I have forked EasyRSS in order to add a way to customize the service used instead of the hard-coded google.com.

The goal is twofold:
* To improve the quality of the Google Reader API in FreshRSS https://github.com/marienfressinaud/FreshRSS/issues/443 by testing it from different clients
* Potentially to revive EasyRSS by offering a completely Open Source client that works with different RSS services, FreshRSS being one of them.
 * That is also the reason why I have removed a bunch of permissions and Google Analytics, to differentiate better from the other clients available.

This pull-request is mainly to initiate the conversation and hear if you could at all be interested by such a thing.

I look forward to read from you.

Best regards,
Alexandre

![screenshot_2014-03-02-17-35-12](https://f.cloud.github.com/assets/1008324/2304613/dd61e240-a22a-11e3-87f3-518f3a8aabca.png)