menu: Write data directory during build instead of with wmaker.inst.

menu: Write data directory during build instead of with wmaker.inst.

Many of the menu files contain the macro #wmdatadir# as a placeholder for
the data directory containing Window Maker themes, styles, background
pixmaps, etc.  This macro is replaced by the the actual path to the data
directory (by default /usr/local/share/WindowMaker) by the wmaker.inst
script, but only when copying WMRootMenu to the user's home directory.

Instead, we replace the macro during the build.  This way, *every* menu
file has the correct path.

Note that several of the files in question were not previously generated
during build.  These have been renamed with a .in extension.