[Camera] Bake camera & view selection

[regcs]

A user on discord requested two features:

• [ ] An option to "bake" the cameras, i.e. create the camera for rendering so that they could be exported to another program.
• [x] An option to have a look through another camera view, i.e. not only through the center camera but any arbitrarily chosen view of a quilt. (this would be handy in case you are preparing a scene, but don't have a Looking Glass available to check the framing from all sides)

This feature request is also connected to #45 and #16. Note that the camera baking would require that for animations all added camera would move and rotate together with the main camera.

[regcs]

Point 2 – being able to look through another camera – was addressed by implementing a blocks-like feature called "Hologram preview" for the Blender viewport: from commit b86e538b3734cb3d75f205cb8b62f9ba8134d3b0 to 31c5f718c307d558ea8a5b50b78341f1ca69d719.