Key bindings for 3rd dimension (up and down)

[EnginEren]

Dear developers,

It's been a great experience for us to host hubs for a scientific conference with many posters lying around the room. Thanks a lot!

We've got some feedback from presenters that it might be a bit easier to have a key for moving up and down. Currently, they enable flying with "G" and then moving up and down by mouse orientations. However, it would be great to have a key pair for moving "directly" up and down.

Cheers,
Engin