New pyroot spells template specializations with [], not ().

Fix reference to MakeNullPointer to work with root 6.22.00.

Delete unused `PyJobOptionsSvc` and related files to avoid migrating it
to the new `IOptionsSvc` interface.

Revert "AthenaPython/Bindings.py: Introduce typed nullptr to deal with return values in case of failures"

This reverts commit c6375548.

AthenaPython/Bindings.py and StoreGateBindings/Bindings.py: Remove workarounds that are (a) not working any more and (b) not needed any more with root v6.22

AthenaPython/Bindings & ROOT 6.22: Adjust dictionary-import syntax, no makeClass any more, drop std::map-pythonization

Remove call to obsolete enable_tree_speedups().

Remove useless SG_BASES declaration for PyObject.
This won't compile after upcoming changes to BaseInfo.

- remove atlas_depend_on_subdirs
- minimize ROOT component dependencies
- update link dependencies

SealSvc does not have any useful function any more

Add condStore() convenience methods to the alg/tool python base classes,
to go with the existing detStore and evtStore.

Delete the `gen/load_typeregistry_dso` functions that could create/load a
`typereg_dso_db.csv` file with type information. However, the generate
function currently just creates an empty file and thus this code seems
no longer necessary.

Remove support for pre-MT thinning (ThinningSvc).

In FilePeekerLib, handle the case where we get a
MetaCont<IOVMetaDataContainer> rather than IOVMetaDataContainer itself.

 - iteritems
 - coerce iterator to list

Use `Python_.*` variables instead of the non-standard `PYTHON_.*`.

Replace `PythonLibs` and `PythonInterp` to the corresponding
`find_package( Python ... )` calls. And remove the dependency entirely
where not necessary.

xrange -> range

When the python code we call gets an exception, we report it by calling
PyErr_Print.  But with python 3, we need to explicitly flush sys.stderr
afterwards; otherwise, the python traceback may never be printed.

Update the handling of CORAL attributes to work with both py3 and py2.
Can simplify it now using a pyroot template proxy.

Remove earlier workaround for std::stream dictionary issues.
The workaround is now causing warnings in the python 3 build.
If the original issue recurs, will need to try to find
a different way to address it.

Temporarily put back handling of BeginRun/EndRun event types to avoid
compiler warning. To be removed once those event types are deleted in
Gaudi.

 - xrange -> range
 - take basestring from past.builtins
 - long
 - take reload from imp
 

begin/endRun and their respective auditor hooks are deprecated.

In python, if TFile.Get fails, it returns a null TObject object, which is
distinct from None.  So comparing the result of Get() against None is wrong;
better to use not or convert to a bool.

This bug caused peeking in certain old data files to fail.
Fixed.

Fix for compilation with python3.

Enable flake8 for all python modules and make them compliant.