Add a Pan method

[Nokse22]

Is your feature request related to a problem? Please describe.
When having an external window there is not method to pan.

Describe the solution you'd like
A Pan method where you pass the delta x and y to pan vertically or horizontally.

Describe alternatives you've considered
Calculate the new camera position and focal point in the external program.

Additional context
Here is the solution thanks to @snoyer that I have in my app.

[mwestphal]

Good point @Nokse22 , good addition idea!