Text: return rendered rectangle from TextRenderer::render().
SceneGraph: code cleanup, documentation, fixed assertions.

The original assertion didn't actually check anything, because the list
was always empty. Moved/copied it to relevant places.
SceneGraph: split object transformations test into more functions.
SceneGraph: allow duplicate occurences in Object::transformations().

Fixes common case where one Object has multiple Drawable features
attached (one for regular mesh and one e.g. debug renderer).
Trade: added forward declaration header.
Trade: defaulted move constructor/assignment.

Hope they will work as expected. Copying is still forbidden, as it
brings serious performance impact for no useful reason.
Primitives: Cube can be now solid or wireframe.
Primitives: Plane can be now solid or wireframe.
Primitives: Square can be now solid or wireframe.
DebugTools: using wireframe primitives in ShapeRenderer.