Make camera spawn position configurable

[caiopiccirillo]

Although PR #10 closed issue #4, the camera position was hardcoded. The camera spawn position needs to be configurable.
The camera should be "adjustable" to some extent, because new 3D models can be loaded into the software and the camera position should be able to show it all.

Proposal:

• Add cartesian (x, y, z) or spherical (ρ, θ, φ) coordinates
• Add camera projection direction hint, such as coordinate origin or geometrical center of model

These configurations should be avaible through graphical interface.