add support for categories (domains) to `StatusCode by using typed
enums and ideas from `std::error_code`.

See merge request gaudi/Gaudi!581

See merge request gaudi/Gaudi!579

See merge request gaudi/Gaudi!578

See merge request gaudi/Gaudi!572

See merge request gaudi/Gaudi!509

This reverts merge request !524

This reverts merge request !524

Closes #5

- Remove IRegistry interface, and define it (for now) as an alias to RegistryEntry
- Remove reference counting from RegistryEntry, replace with std::unique_ptr
- Add move constructor/assignment to RegistryEntry

See merge request gaudi/Gaudi!524

See merge request gaudi/Gaudi!526

The syntax of
```
  ToolHandle<IMyTool> m_tool;
  bool m_useToolFlag;
...
  ATH_CHECK( m_tool.retrieve( DisableTool{ !m_useToolFlag } ));
```

Add another TaggedBool to  make it a little clearer what are people's
thoughts on `DisableTool / EnableTool` vs.
`DisableToolIf / EnableToolIf`:
```
   ATH_CHECK( m_tool.retrieve( EnableTool{ m_useToolFlag } ));
```

The StatusCode now consists of a value and category/domain. By default
StatusCodes are created within a "default category". But users can
define new categories and StatusCodes using typed enums. The design is
mainly borrowed from std::error_code.

Main changes:
- StatusCode::setCode has been removed
- No implicit conversions from/to bool or int anymore. This greatly
  increases type safety.
- Converted all unscoped enums in Gaudi to their own StatusCode
  category (Clients will have to adjust their code to the scoped enum
  names (e.g. ERR -> Status::ERR)
- Added operator bool() that is equivalent to isSuccess()
- Added ternary (bitwise) AND(&) and OR(|) operators to combine
  StatusCodes according to three-valued logic
- Added extensive unit tests for all StatusCode features

Impact on clients:
- Code that relies on the implicit StatusCode<->bool/int conversion has
  to be changed to explicitly construct/convert StatusCodes via either
  the constructor, operator bool() or getCode().
- Clients using Gaudi StatusCodes need to adjust to using the scoped
  enums. E.g. clients of the ConversionSvc need to change BAD_STORAGE_TYPE to
  Status::BAD_STORAGE_TYPE when checking for specific StatusCode return
  types.

- Use !571 to support Ranges and Selections
- Update examples to use Ranges and Selections
- Tweak invoke,deref

Add support for Gaudi::Range_ to DataObjectHandle

See merge request gaudi/Gaudi!571

add TimelineSvc-based implementation of 'last running schedule' detection (used in scheduler state dumps)

register (partial) timeline events as early as possible - right before the start of Algorithm::execute()

TaggedBool: use a more specific header guard name

See merge request gaudi/Gaudi!584

[[ deprecated ]] does not compile with using statements

See merge request gaudi/Gaudi!587

make uncompiled exported headers compilable

See merge request gaudi/Gaudi!590

Demoted a few AvalancheSchedulerSvc messages

See merge request gaudi/Gaudi!576