viewer: drop that fugly FPS counter.

Will be done better (HUD) via DebugTools sometime in the future, now
this just unnecessarily bloats the example.
viewer: no `using namespace` for Magnum subnamespaces.
viewer: no need to use std::unique_ptr.

The way it was used was weird anyway.
viewer: drop additional files.

They aren't too big to be in separate file.
viewer: minor code cleanup.
viewer: display mesh name in log.

Also modify the output so it doesn't look like the optimization takes
whole time (the import does).
viewer: rewritten using ResourceManager.

Simpler (but slightly longer) code, more extensible and failure proof.
viewer: minor cleanup.
viewer: removed key controls, wireframe and Tipsify optimization.
viewer: print also scene and material names.
viewer: use `importer` instead of `colladaImporter`.

Might use e.g. OBJ importer in the future.
viewer: renamed ViewedObject to ColoredObject.

Will have also textures ones.
viewer: more cleanup.
viewer: support for diffuse texture.