Create CMake files for several packages

This remove the CMake configuration of several larger packages and places
it into their own files in the Modules/Packages folder.
 - COMPRESS
 - KIM
 - LATTE
 - MESSAGE
 - MSCG
 - USER-MOLFILE
 - USER-NETCDF
 - USER-PLUMED
 - USER-QMMM
 - USER-QUIP
 - USER-SCAFACOS
 - USER-SMD
 - USER-VTK

cmake/Modules/Packages/USER-MOLFILE.cmake

@@ -0,0 +1,10 @@
+if(PKG_USER-MOLFILE)
+  set(MOLFILE_INCLUDE_DIRS "${LAMMPS_LIB_SOURCE_DIR}/molfile" CACHE STRING "Path to VMD molfile plugin headers")
+  add_library(molfile INTERFACE)
+  target_include_directories(molfile INTERFACE ${MOLFILE_INCLUDE_DIRS})
+  # no need to link with -ldl on windows
+  if(NOT ${CMAKE_SYSTEM_NAME} STREQUAL "Windows")
+    target_link_libraries(molfile INTERFACE ${CMAKE_DL_LIBS})
+  endif()
+  list(APPEND LAMMPS_LINK_LIBS molfile)
+endif()