Add manual focus and exposure buttons and navigate arrows on Control tab

Feature request

Summary

Several people on the forum requested a +- z-axis button on the `navigate page of the web app. This is either because they are using touchscreen, or because the keyboard shortcuts are not well publicised.

There sidebar has only a few items, so there is space for [focus up] and [focus down] buttons. (with mouseover saying page up and page down)

There is probably space for a software cursor pad, but click-to-move exists for a calibrated stage.

Putting a [brighter] and [darker] and/or [auto exposure] button here would be great as well. links to #240