I've fixed hiding and showing pinned messages in the menu, but not everything is as smooth as I would like.

In the current test build, clicking on “Hide pinned message” in the three-dots menu will result in a crash. In the next test build this will be fixed and will work as it should. However, I haven't yet been able to fix the “Hide” button in the window that appears when you click X in the pinned messages panel. But at least it won’t cause the app to crash.

Along with that, if you've stumbled upon a crash when editing a local folder, I glad to say that I fixed that too. So at least there should be no more crashes (if there are still any, please report it!).

Other fixes that will be in the next test build:
— Build fixes for Linux (authored by @Shlyupa), unless it'll turn out that I forgot to port something or broke something else;
— Fixes for text in sliders in settings: now on the default white theme you will see what does this option do.