See merge request !1529

See merge request !1528

See merge request !1527

See merge request !1520

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

Remove remaining Python2 backwards-compatibilty code.

Appending to an empty default HandleArray was not possible. Fix and add
unit test.

See merge request !1503

Remove deprecated `OutStreamType` property from `ApplicationMgr` and
`MinimalEventLoopMgr`.

Make the printout of `set` properties reproducible. For GaudiConfig2,
this is done via the property `repr` itself. For the legacy
Configurables, only in the `str` printout.

See merge request !1525

See merge request !1524

See merge request !1518

Closes #282

See merge request !1522

To support `Gaudi::Property<DataOjbIDColl>` we need to allow implicit
conversion from `tuple`.

Allow only `list` types to be assigned to `list` properties and extend
test coverage. This brings GaudiConfig2 in line with the legacy
configurables. I.e. the following now fails:
```
  MyAlg.MyVecOfStrings = "abc"
```

See merge request !1519

See merge request !1513

See merge request !1516

See merge request !1515

See merge request !1512

For backwards compatibility, allow the following code:
```
   alg.MySetProperty = [1, 2, 3]
```

Change the Python type of `std::unordered_set` properties from `list` to `set`.
Parsers only required minor updates and special treatment of the empty
set, which can only be represented as `set()` in Python (`{}` is
reserved for dictionaries).

This will certainly break client code, i.e.
```
   MyAlg.ExtraInputs += ['foo']
```
will have to be updated to
```
  MyAlg.ExtraInputs.add('foo')
```

For the moment only `std::unordered_set` is mapped to a Python `set`.
Regular `std::set` remains as Python `list` to maintain insertion order.

See merge request !1517

Fix the cleanup function and extend the test to `dict` and `list`
proprties. Also migrate to `pytest` fixtures and exception handling.

See merge request !1514