[Added] Google Test as unit test framework.

Google Test is a xUnit test framework for C++. It has been added in
the utils/gtest-1.6.0 folder. Build system has been updated to build
and link in the Google Test framework.

Running unit tests can be done by running core3 with the command line
argument 'runUnitTests'.

Change-Id: Ie92b2fc209122a294b6363087eb84104fdf89eb0