Remove labels from filter button on toolbar

[CatMe0w]

This is related to #498, #550, #572.

With the default width of the sidebar, clicking the filter button on the toolbar will make the button disappear from the sidebar area, ending up in the rightmost corner:

Technically, it works as intended, but it's very confusing from the perspective of users: it looks like the buttons just disappear. Dragging the sidebar to make it wider can reveal the buttons, but it's not intuitive. Actually, I got stuck here for a few days, trying to figure out where my beta versions went.

I think we might avoid the overflow entirely, and I tried some different approaches like using abbreviations instead of full text such as "Release only," but the overflow still happens and does not look good:

Finally, I found that completely removing the labels could be the most ideal solution. A filled, highlighted button with floating help text could be intuitive enough and won't break the consistency of the UI:

I hope this change improves the user experience and keeps the UI clean and functional.

[CatMe0w]

This pull request is now obsolete with the v3.0 release.