Icon & executable description for mingw

Updated the makefiles to build ico.o from ico.rc when compiling under Windows, such that MinGW executables also get a nice icon and file description.
This might need some testing to verify that it works with Linux (particularly Wine?) as well. Tested with MinGW.

The second patch moves version.h out of ALL.h, as only two files (AM.cpp and ico.rc) need version.h. This reduces the amount of files that need to be rebuilt when changing the version.