Update SDK/Tools to latest, use Maven instead of git submodule for FB SDK

- Removed the facebook-sdk submodule.  Let's use Maven (dependencies automatically resolved by Android Studio) because it's a lot cleaner.
- Updated Android build tools and support library to latest.
- Raise minSdkVersion to 9 to match latest Parse SDK.
- Updated the README to only focus on setup instructions for Android Studio, which is becoming the more preferred IDE instead of Eclipse.
  * `parse_app_id` and `parse_client_key`
  * `facebook_app_id`
  * `twitter_consumer_key` and `twitter_consumer_secret`