gaudi_add_compile_test can be used to add tests that check for the
existence of (expected) compilation failures. Use this to implement a
unit test to check for StatusCode comilation failures.

Closes #14

See merge request gaudi/Gaudi!546

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

See merge request !581

See merge request !579

See merge request !578

See merge request !572

See merge request !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 !524

See merge request !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 !571