* Calling enable_testing() only in root path.
* Using CORRADE_CXX_FLAGS instead of our own set to make things easier
to maintain.
* Various cleanup and reorganization.
Functionality present in Object is now split into three main components:
* Object itself, handling parent/children relationships
* Transformation implementation and interfaces for common functionality
* Object features, providing transformation caching and base for
cameras, collision shapes, rigid bodies etc.
Some functionality depending on former implementation is temporarily
disabled and will be reworked later.
* CMAKE_SHARED_LIBRARY_CXX_FLAGS is empty here, caused CMake errors.
* CMake's OBJECT target has a bug that it doesn't define target_EXPORTS
as with other library targets, so it's needed to define it manually.
It also fixes empty flags issue.
* Visibility headers weren't updated for OBJECT targets, they now also
catch *Objects_EXPORTS defines.
Reusing macros MAGNUM_EXPORT and friends already used for Windows
builds. For exported classes added MAGNUM_LOCAL to private members which
are not referenced from any inline function. Added explicit
MAGNUM_EXPORT to private members which are referenced. CMake provides
its own macro <target>_EXPORTS, using that instead of
set_target_properties().