Hiding apps from Launcher's app-drawer

This is another suggestion by Claude Cesa, who reached out to me in an e-mail:

A useful feature would be to allow hiding apps from the app-drawer.

I implemented this as part of my fork. Since many of the changes I made are a matter of taste (and this repo doesn't seem to be actively maintained any more) I decided not open a PR but just publish it as a separate app.