Atlas extensions

This MR rolls up many improvements in FullSimLight and FSL. Chief among those are input from HEPMC3 files, plugins for physics lists, improvement of the graphical user interface, and a reorganization of much of the ATLAS extension code so that the atlas customizations move out of fullsimlight proper and into plugins.

ATLAS-Extensions/ATLASMagneticFieldMapPlugin/cmake/BuildType.cmake

+
+# Author: Marcus D. Hanwell
+# Source: https://blog.kitware.com/cmake-and-the-default-build-type/
+
+# Set a default build type if none was specified
+set(default_build_type "Release")
+
+# TODO: at the moment, we want to build in Release mode by default,
+# even if we build from a Git clone, because that is the default mode
+# for our users to get the source code.
+# But maybe we will want to change this behavior, later?
+# if(EXISTS "${CMAKE_SOURCE_DIR}/.git")
+#   set(default_build_type "Debug")
+# endif()
+
+if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+  if( COLOR_DEFS )
+    message(STATUS "${Blue}INFO: Setting build type to '${default_build_type}' as none was specified.${ColourReset}")
+  else()
+    message(STATUS "INFO: Setting build type to '${default_build_type}' as none was specified.")
+  endif()
+  set(CMAKE_BUILD_TYPE "${default_build_type}" CACHE
+      STRING "Choose the type of build." FORCE)
+  # Set the possible values of build type for cmake-gui
+  set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS
+    "Debug" "Release" "MinSizeRel" "RelWithDebInfo")
+endif()
+