Maven compatibility

Adding pom files to build the facebook android-sdk and install it in the local maven repository.

This adds support for running the build with 'mvn clean install' from the root and as a result having the facebook-android-sdk get installed in your local repository.

Unfortunately, I haven't been able to get the tests to pass locally, so I excluded those from the mvn build for now. With a config.json file, the tests hang on com.facebook.AsyncRequestTests#testBatchUploadPhoto. Without the config.json file, the build completes, but 115/232 tests fail.

Given that neither the build_and_test script nor configure_unit_tests were able to be run out of the box (see #281), I'm not too surprised that I'm having these other testing problems.