Zooming using +, - does not work when controls or features are focused

[AliyanH]

Suggestion:

When the focus is on the controls (i.e. zoom in button, zoom out button, etc.) - we can support the use of arrow keys to work alongside tab (down or right arrow) and shift-tab (left or up arrow) to navigate the controls. Do you think this would be an appropriate improvement to make?

Similarly, the + and - keys only work when the map is focused, we can expand this to allow the use of +,- when focus is elsewhere as well.

Originally posted by @AliyanH in #160