Externals / Analysis Release LCG_100 Update, master branch (2021.05.17.)

Updated all projects to atlasexternals-2.0.107. The full list of changes wrt. atlasexternals-2.0.106 is the following (atlasexternals@2.0.106...2.0.107):

• Updated AnalysisBaseExternals to use external versions in sync with LCG_100;
  • Introduced simple patches for KLFitter and BAT to make them compatible with ROOT 6.24/00;
  • Upgraded Boost to version 1.75.0;
  • Upgraded HDF5 to version 1.10.6;
  • Upgraded libxml2 to version 2.9.10;
  • Upgraded nlohmann_json to version 3.9.1;
  • Upgraded Cython to version 0.29.21 and pip to version 21.0.1 (both as part of the PyAnalysis package);
  • Upgraded XRootD to version 5.1.1;
    • Building OpenSSL 1.1.1 for XRootD, if it is not available on the build system already;
  • Upgraded ROOT to version 6.24/00.
• Introduced the PRIVATE_WORKING_DIRECTORY option for atlas_add_test(...) (thanks to @fwinkl);
• Made FindGaudi.cmake compatible with the latest Gaudi master version, fixing gaudi/Gaudi#180 (closed).

At the same time I upgraded the AthAnalysis build to use LCG_100_ATLAS_1 in sync with all the other releases, and updated 2 Top Physics packages to be compatible with ROOT 6.24/00.