OSRE-Ed: Add meshes to the scene

**Is your feature request related to a problem? Please describe.**
As a user, I want to be able to add meshes to the scene.

**Describe the solution you'd like**
Via the menu ,it shall be able to add meshes to the scene. The first mesh shall be just a cube.

**Describe alternatives you've considered**
N/A

**Additional context**
N/A