Verified that it updates once it gets focus
Verified the timer stops when window doesn't have focus
Has the side-effect that when you have multiple windows visible at the same time (e.g. two windows next to each other) that only the active one will update its free space info live
Creating a `MountPointObserver` will eventually query `KMountPoint` which `statvfs` the file system and potentially block. So, perhaps this should be changed to not destroy but just tell it to "not update"? or have a refcount for "active listeners" as well? oof..
Even pressing Alt+Tab causes the window briefly to lose focus (X doing a short grab), so this needs some further work
Also doesn't do anything wrt tabs, if you have multiple tabs open, all of them still update, even when not current