Filters: Add zoom buttons to location map

[danieldegroot2]

What feature would you like to see added?

Add zoom in/out buttons to the location search / bounding box (bbox) map in the Filters form page.

additionally, scroll to zoom amount could be increased / made more sensitive (#504)

Also, when focused on this map, Up/Down arrow (otherwise used for changeset list navigation) / WASD on keyboard or (ctrl/shift+) middle mouse button could be used for continuous horizontal/vertical/omnidirectional map navigation.

(update the about hotkey section if needed)

Related #686/#639/#401.

Why would this be useful to you or other users?

It would allow the user to more quickly zoom in once over the approximate area. (it is a common feature on digital maps, regular and embedded, also small ones)

Currently the user has to slowly zoom in(/out) to the map using the (CTRL Control +) Mouse Up/Down mouse scroll wheel, which takes numerous scrolls (regardless of angle to the globe). The user can alternatively use double mouse click, which is faster, but does not allow to zoom out as far as I know. They could also change their mouse scroll wheel sensitivity, but this may impact other applications.

Furthermore, many flat maps also allow quickly zooming in with Shift+Drag(left mouse button), but globe version does not..