Merge build systems

[EinMByte]

I think it's time to pick one build system instead of maintaining both cmake and the Makefile.
The Win32/ folder will soon be removed since the Visual Studio project is no longer supported. CMake can be used on Windows instead, but we need more people to test on Windows.

Personally I'm more experienced with cmake, but I am prepared to stick with the Makefile if required.

[EinMByte]

I will go ahead and remove everything except cmake.
Simultaneously, I will try to introduce a stronger separation between the client (BOB, SAM, I2PControl, HTTPServer, HTTPProxy, ...) and the core router (transports, tunnels, netDB, ...).
The core will be organized as a library that is directly usable in C++ software.
Both parts will be put into separate directories.