Enhance accessibility

[Steeven9]

• added preventUnload on refresh and back button to avoid navigating away by mistake
• make texts more readable by increasing contrast
• made checkboxes in the terrain section mirrored for enhanced layout and aestethics
• wrote description of the PR

[Fireblast9]

Great work, however as a user I currently get prompted about confirmation to leave even when there is nothing on the page, it would make more sense to have something like a boolean or a flag that checks whether the user actually has something worth preventing losing.

Also maybe it would be nice to prompt the user also on the "back" browser button (if possible, otherwise disregard this)