Books with lots of categories start to render the category labels offscreen

[DaFuqs]

Is your feature request related to a problem? Please describe. Books with lots of non-hidden categories have their category labels on the left part of the screen visually overflow downwards, until they start rendering offscreen. This looks weird, or even makes the categories unusable, since the player can't click on the icons that are offscreen.

Describe the solution you'd like Handling more category tabs that the gui can render more gracefully, like via an overflow menu or pagination.