CMake for Windows

* Delete unused pkg-config include
* Fix *_DIR variables for Windows
* Define VCMI_DLL for libvcmi
* Define M_PI (sometimes M_PI may be undefined, even with _USE_MATH_DEFINES, <cmath> and -std=c++0x)
* Disable WIN32 flag for executables
* Fix libvcmi linkage
* Fix vcmiclient linkage
* Fix CVideoHandler compilation
* Fix .dlls and .exes filenames