Remove expat dependency, Fixes #5 . Fix gmock/gtest build.

* Change std::string/const char * to QString in a few more places
* Use QDir functionality to create directories in Cluster::makeDirs()

Note: this commit is reverting the change to gmock 1.7, since I had the patch necessary to make version 1.6 install respect the INSTALL_DIR parameter.
      Now the gmock 1.6 should download, build and correctly install itself into 3rd_party/lib and 3rd_party/include directories.