Changes Google APIs Client Library for Objective-C

- *Google-API-Client* => We have added multiplatform support (iOS and Mac OS X) because this library is compatible with applications built for iOS 3+, and Mac OS X 10.5+. Added real dependencies to *GTMHTTPFetcher*, *gtm-oauth2* and *SBJson*. ARC isn´t required. Added all *Google APIs Client Library* services.
 
- *gtm-oauth2* => Added *GTMHTTPFetcher* as real depedency. ARC isn´t required. Adopting safer copy phase for source files because the spec is point to HEAD.
  
- *GTMHTTPFetcher* => Currently, the Google´s library *gtm-http-fetcher* isn´t included as independent Pod.

We also emailed Google to explicitly ask them to support tag in their repository to better manage cocopods.