Added "uninstall" script

Here is the cmake documentation:
http://www.cmake.org/Wiki/CMake_FAQ#Can_I_do_.22make_uninstall.22_with_CMake.3F
Don't install gtest.

Gtest is only needed for the tests, so we don't
install the library but refer to the local build
directory.
Merge branch 'master' into uninstall
Removed unused lgtest parameter.
Merge pull request #74 from simongog/uninstall

Added "uninstall" script