Add Zoom slider

[jidanni]

Perhaps add a "zoom slider" as seen in https://www.offline-maps.net/en/help as an additional method of zooming. Some users say that after using it they don't want to go back to any other way of zooming.

[sarvesha-jaiswal]

hello I want to work on this issue, I've reached here through GSoC. Can I work on this?

[simonpoole]

@sarvesha-jaiswal feel free to implement this, you will need to add a preference so that the zoom buttons or a slider can be used-