Updates the cmake build system

It's still has some work, but it successfully builds on
all 3 main platforms.  Some of the outstanding items
include:

   Install target testing (mostly important for Linux)
   CMakeList clean up and comments
   Debug and Release build verification
   Audit of compile/link options
   Need a Mac signed and notarized build
   (and probably more)

plug-ins/CMakeLists.txt

@@ -0,0 +1,59 @@
+
+set( TARGET plug-ins )
+set( TARGET_ROOT ${topdir}/plug-ins )
+
+message( STATUS "========== Configuring ${TARGET} ==========" )
+
+def_vars()
+
+list( APPEND SOURCES
+   SilenceMarker.ny
+   SoundFinder.ny
+   SpectralEditMulti.ny
+   SpectralEditParametricEQ.ny
+   SpectralEditShelves.ny
+   StudioFadeOut.ny
+   adjustable-fade.ny
+   beat.ny
+   clipfix.ny
+   crossfadeclips.ny
+   crossfadetracks.ny
+   delay.ny
+   equalabel.ny
+   highpass.ny
+   limiter.ny
+   lowpass.ny
+   noisegate.ny
+   notch.ny
+   nyquist-plug-in-installer.ny
+   pluck.ny
+   rhythmtrack.ny
+   rissetdrum.ny
+   rms.ny
+   sample-data-export.ny
+   sample-data-import.ny
+   tremolo.ny
+   vocalrediso.ny
+   vocoder.ny
+)
+
+foreach( source ${SOURCES} )
+   set( src "${_SRCDIR}/${source}" )
+   set( dst "${_EXEDIR}/${TARGET}/${source}" )
+
+   add_custom_command(
+      DEPENDS
+         "${src}"
+      COMMAND
+         ${CMAKE_COMMAND} -E make_directory "${_EXEDIR}/${TARGET}"
+      COMMAND
+         ${CMAKE_COMMAND} -E copy "${src}" "${dst}"
+      OUTPUT
+         "${dst}"
+   )
+
+   list( APPEND OUTPUTS "${dst}" )
+endforeach()
+
+add_custom_target( ${TARGET} ALL DEPENDS ${OUTPUTS} SOURCES ${SOURCES} )
+