Introducing the actual navmesh creation functions

- At the moment only support the creation of tiled navmesh
Allow the configuration of offmesh connections in dtTiledNavmeshCfg
dtCrowd::init now only requires a const navmesh
Making the crowd tests rely on DetourNavmeshCreator
Renaming `DetourCrowdTestUtils` to `Utils`
Improving the dtMesh

- Copy constructor and assignment operator
- face retrieval method
Replacing crowd demo navmesh creation with DetourNavmeshCreator
Removing the now obsolete DetourSceneCreator library
Introducing a U-turn test environment and sample