Remove `print_function`, `absolute_import` and `division` imports.

- 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

- moved the report logic to DHHVisitor
- print list of inputs and outputs of an algorithm only once
- do not print "data dependencies" header if there is none
- use DHHVisitor to report DataHandle owners in AvalancheScheduler

Change explicit mention of Python binary to python3
which should be supported by all distributions and
environments (https://peps.python.org/pep-0394/).

Update hash bangs to python3.

Adapt CMake to search for pytest also as pytest-3; likewise
for nosetest binary as nosetests3 (with fallback to
pytest and nosetests, which can be used in some
virtual environments, even with a Python 3 install).

Remove unnecessary utf-8 encoding lines.

Update test scripts to python3

plus minor fixes

so that things work in a super project build