Reorganize subdirectory layout

The original directory layout comes from the NINJAM source code that Wahjam forked.

After substantial changes, mostly due to converting code to use the Qt framework and dropping platform-specific code, it's time to clean up the source tree.

The new layout puts core code into common/, GUI client code into qtclient/, and server code into server/.  There is also a top-level Qt project file.  It is finally possible to build everything with just:
    cd wahjam && qmake && make

I also cleaned up and eliminated some code to make the subdirectory reorganization easier.  The WDL random number generator and SHA1 code is no more - Qt provides equivalent functionality.