* hide use of std::mutex from /clr compilation under Visual Studio

C++11 <mutex> is not available when compiling with  /clr under Visual Studio, thus opencv cannot be easily included.
It is fixed by making a CEEMutex wrapper class, around an opaque implementation using std::mutex internally

* fixed compilation outside of Visual Studio

fixed compilation outside of Visual Studio by avoiding some macros

* fixed indentation, prepare getting rid of CEEMutex/CEELockGuard

fixed indentation
After discussion, CEEMutex and CEELockGuard can be totally removed, letting the developer in a /clr context to provide his own implementation

* remove CEEMutex/CEELockGuard