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.
This doesn't seem necessary. Gradle warnings should be enough for those who do not have it and we won't have to make sure this is up to date at all times.