Added a new file for recording minimal dependency versions.
Bumped minimal CMake version to 2.8.7.
Removed CMake version checks that we don't need anymore.
Dropped OpenCVConfig.cmake - we don't use it anymore.
Removed OpenCVFindPkgConfig.cmake, since it's bundled with CMake now.

In fact, I don't think we actually use it... but I kept the include,
just in case.
Removed CMakeParseArguments.cmake, which we don't use.

It's part of CMake nowadays, too.
Removed obsolete CMake workaround.
Inlined the getMD5 macro, which no longer saves us anything.
Merge pull request #1238 from SpecLad:cmake-min-ver