Disabled unit tests involving GUI for now.
Workaround with qt5_use_modules in CMake.

Travis CI uses CMake version 2.8.7.
Tell `.travis.yml` to install gcc 4.8
Fix `.travis.yml` by updating apt repos first.
Added debug message for proper build with Travis.
Attempting to fix gcc version getter in cmake.
Disabling build with clang in travis
Attempt to fix gcc version getter in CMake
Retrying again

using:
http://root.cern.ch/svn/root/trunk/cmake/modules/CheckCompiler.cmake
Small cleanup of `DOConfigureCompiler.cmake`
Small compilation fix found by Travis using gcc
Fix typo in `DOConfigureCompiler.cmake`
Renamed DO++ to DO-CV
Updated README.md layout.
Updated third-party section in README.md
Show Travis build status in README.md
Small update in README.md
Reformatting of `.travis.yml` config file.
Small fix in `travis.yml`.
Updated `.travis.yml`: parallel build and unit testing.