Added the LayoutTestsRunner class that is responsible for running the tests....

Added the LayoutTestsRunner class that is responsible for running the tests. Also, added some methods to FileFilter.

It preloads the tests from the given path, runs them and asks for dumps and diffs. It will also prepare summaries in the future. It delegates
most of the work of actually running the individual tests to LayoutTest class and AbstractResult (and its subclasses in the future).

Change-Id: I483bf26a380b539e4769e61b4a09fa270ab0e8e9