Library Project including GridLayout.

This can be used by an Android project to provide
access to GridLayout on applications running on API 7+

There is technically no source, but the src folder is necessary
to ensure that the build system works. The content is actually
located in libs/android-support-v7-gridlayout.jar
Add readme for gridlayout project library.
Add readme for gridlayout project library.

Change-Id: Ic64ff2ee2623f954d6db79056a4fd100356a1021
