CMake Refresh

I've refreshed CMakeLists.txt to
- Use OpenCVConfig.cmake (maintained by OpenCV) instead of the custom FindOpenCV.cmake which is non-standard. This method has less complicated linking in CMakeLists.txt as well.
- Add a Doxygen 'doc' target when the Cache variable is set (off by default). Doxygen comments to come.
- Compile at /W3 or -Wall (we have no warnings at those levels at the moment, we should try to keep it that way).

There were a few accompanying changes (.gitignore, a placeholder mainpage for Doxygen, etc).

Note: Qt changed a bunch of whitespace tabs to spaces. To see the diff in github without whitespaces, append "?w=1" to the url.