- move Gaudi::Funtional to GaudiFunctional subdir
  - headers are now under "Gaudi/Functional"
  - legacy GaudiAlg corresponding header redirect to the new ones
- replace GaudiAlgorithm with Algorithm wherever possible in tests and
  utilities
- add Gaudi::Sequencer basic implementation to replace GaudiSequencer
- move GaudiAlg specific tests, examples, dictionaries and Python modules
  to GaudiAlg subdir
- add CMake option GAUDI_ENABLE_GAUDIALG to allow skipping GaudiAlg
  (default to true)
- minor fixes and clean ups

This is a follow up of !1354. There PkgConfig is only looked up if
the `pkg_check_modules` macro hasn't been define. The problem is that
the scope of macros seem to be global, and finding PkgConfig in another
directory defines that macro. However, variable scope is per directory
and the cmake of PkgConfig doesn't really work.

This changes the check to use the `PKG_CONFIG_FOUND` variable

At build time the requested optional dependencies are "REQUIRED", while
they are just RECOMMENDED when in GaudiConfig.cmake is used in
downstream projects.

this allows to point CMake to a version of Python of our choice,
despite what is available on the PATH.

Thomas Cluzel authored 4 years ago and Marco Clemencic committed 4 years ago

see https://its.cern.ch/jira/browse/LBCOMP-23



Co-authored-by: Marco Clemencic <marco.clemencic@cern.ch>