.gitignore:
- Ignore external glew project.

CMakeLists.txt:
- Added glew as an external project.
- Now cmake will try to find versions of 3rd party software in the system and if found use them. Otherwise dependencies will automatically download and build our hosted versions. Currently this only holds glew, because with gtest, even if we find a version in the system, we don’t use it, because the gtest people didn’t use cmake correctly.

cmake/toyrenderer_inject_variables.cmake.in:
- Added CMAKE_PREFIX_PATH to the cached variables of the toyrenderer project, which points to the glew project. This way the headers and libs of glew are found, when compiling toyrenderer.
CMakeLists:
- Compiles under Mac OS X Mavericks and Ubuntu 12.04.
- Moved to Qt5 as Qt4 does not support Mavericks.
- Changed minimum required version of cmake to 2.8.7, which is default in Ubuntu 12.04.
- Ignoring installed versions of GTest, because the official cmake config is broken IMHO.
- Changed the clone URL from th git@github... version to the https-version, because I
  think anonymous clones are only possible with https?
- If the system installation of a 3rd party lib shall be used, we create a phony
  ExternalProject for this lib to satisfy dependencies of other ExternalProjects.
- The FindGLEW.cmake module is not available in 2.8.7, but it looks like a simple
  find_library() is enough for the glew lib. Changed find_package() to find_library().

cmake/FindGTest.cmake:
- The module will not terminate anymore, if GTest is not found. For dependent projects
  this behaviour was desired, but now we use it in the top-level to determine whether
  to use the system installation or to compile our own.