looks some ugly on devices with square screen

# IMPORTANT
* App version: 2.16.1
* Android version/rom: 16
* Device: uniheartz titan 2
* I accept that this issue will be closed without further notice in case I didn't describe the problem including general information, or didn't [search](https://github.com/gsantner/markor/issues?q=) for similar issues & [requests](https://github.com/gsantner/markor/discussions?discussions_q=).

## Explain the Problem

The interface looks ugly on devices with a square screen. In this case, the bottom panel. See screenshot. I'd like to be able to at least hide the panel key labels and thereby reduce the panel's height.


Reproduce the layout problem on a square-screen Android device using the attached screenshot as the visual reference. Locate the bottom panel implementation and determine how its labels and height respond to the available width; the issue is done when the panel is usable and can hide its key labels or otherwise fit the square layout without obscuring controls.

Written by the indexing model from the issue text.