Update of NEST package

This update adds NEST 3.0 and fixes some broken dependencies for older versions.

packages/nest/2021-07-17_fix-pyexecdir.patch

+diff --git b/CMakeLists.txt a/CMakeLists.txt
+index d879164a8..e92b21e70 100644
+--- b/CMakeLists.txt
++++ a/CMakeLists.txt
+@@ -83,7 +83,7 @@ set( target-bits-split "standard" CACHE STRING "Split of the 64-bit target neuro
+ ################################################################################
+ 
+ # In general use the CMAKE_INSTALL_<dir> and CMAKE_INSTALL_FULL_<dir> vars from
+-# GNUInstallDirs (included after calling nest_process_with_python()), but the 
++# GNUInstallDirs (included after calling nest_process_with_python()), but the
+ # CMAKE_INSTALL_DATADIR is usually just CMAKE_INSTALL_DATAROOTDIR
+ # and we want it to be CMAKE_INSTALL_DATAROOTDIR/PROJECT_NAME
+ set( CMAKE_INSTALL_DATADIR "share/${PROJECT_NAME}" CACHE STRING "Relative directory, where NEST installs its data (share/nest)" )
+@@ -130,6 +130,7 @@ nest_set_default_compiler_flags()
+ #            of GNUInstallDirs defining CMAKE_INSTALL_<dir> and CMAKE_INSTALL_FULL_<dir>.
+ nest_process_with_python()
+ include( GNUInstallDirs )
++nest_post_process_with_python()
+ nest_process_with_optimize()
+ nest_process_with_debug()
+ nest_process_with_intel_compiler_flags()
+diff --git b/cmake/ProcessOptions.cmake a/cmake/ProcessOptions.cmake
+index 1d69c1a84..7e47db25b 100644
+--- b/cmake/ProcessOptions.cmake
++++ a/cmake/ProcessOptions.cmake
+@@ -399,25 +399,25 @@ function( NEST_PROCESS_WITH_PYTHON )
+         execute_process( COMMAND "${Python_EXECUTABLE}" "-c"
+           "import sys, os; print(int(bool(os.environ.get('CONDA_DEFAULT_ENV', False)) or (sys.prefix != sys.base_prefix)))"
+           OUTPUT_VARIABLE Python_InVirtualEnv OUTPUT_STRIP_TRAILING_WHITESPACE )
+-          
++
+         if ( NOT Python_InVirtualEnv AND CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT )
+           message( FATAL_ERROR "No virtual Python environment found and no installation prefix specified. "
+             "Please either build and install NEST in a virtual Python environment or specify CMake option -DCMAKE_INSTALL_PREFIX=<nest_install_dir>.")
+         endif()
+-      
++
+         # Setting CMAKE_INSTALL_PREFIX effects the inclusion of GNUInstallDirs defining CMAKE_INSTALL_<dir> and CMAKE_INSTALL_FULL_<dir>
+         get_filename_component( Python_EnvRoot "${Python_SITELIB}/../../.." ABSOLUTE)
+         set ( CMAKE_INSTALL_PREFIX "${Python_EnvRoot}" CACHE PATH "Default install prefix for the active Python interpreter" FORCE )
+       endif ( CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT )
+ 
+-      set( HAVE_PYTHON ON PARENT_SCOPE )
+-
+       # export found variables to parent scope
++      set( HAVE_PYTHON ON PARENT_SCOPE )
+       set( Python_FOUND "${Python_FOUND}" PARENT_SCOPE )
+       set( Python_EXECUTABLE ${Python_EXECUTABLE} PARENT_SCOPE )
+       set( PYTHON ${Python_EXECUTABLE} PARENT_SCOPE )
+       set( Python_VERSION ${Python_VERSION} PARENT_SCOPE )
+-
++      set( Python_VERSION_MAJOR ${Python_VERSION_MAJOR} PARENT_SCOPE )
++      set( Python_VERSION_MINOR ${Python_VERSION_MINOR} PARENT_SCOPE )
+       set( Python_INCLUDE_DIRS "${Python_INCLUDE_DIRS}" PARENT_SCOPE )
+       set( Python_LIBRARIES "${Python_LIBRARIES}" PARENT_SCOPE )
+ 
+@@ -431,7 +431,6 @@ function( NEST_PROCESS_WITH_PYTHON )
+           set( CYTHON_VERSION "${CYTHON_VERSION}" PARENT_SCOPE )
+         endif ()
+       endif ()
+-      set( PYEXECDIR "lib/python${Python_VERSION_MAJOR}.${Python_VERSION_MINOR}/site-packages" PARENT_SCOPE )
+     endif ()
+   elseif ( ${with-python} STREQUAL "OFF" )
+   else ()
+@@ -439,6 +438,12 @@ function( NEST_PROCESS_WITH_PYTHON )
+   endif ()
+ endfunction()
+ 
++function( NEST_POST_PROCESS_WITH_PYTHON )
++  if ( Python_FOUND )
++    set( PYEXECDIR "${CMAKE_INSTALL_LIBDIR}/python${Python_VERSION_MAJOR}.${Python_VERSION_MINOR}/site-packages" PARENT_SCOPE )
++  endif()
++endfunction()
++
+ function( NEST_PROCESS_WITH_OPENMP )
+   # Find OPENMP
+   if ( with-openmp )