Add command to "jump" to specific window

[hertg]

Add a command/keybind to directly jump to a specific window in the currently visible windows (eg. with mod + ctrl + <nr>).

Additionally, maybe we could even implement an overlay and display the windows' index when mod + ctrl is held down. Then the user can immediately see the index of the window they want to jump to. This could look something like below:

The overlay would probably depend on #495.

Motivation I was thinking about that in the past weeks, because I still struggle sometimes with the window order in certain layouts, so it is not immediately clear to me if I should move up or down to go to the desired window. Also, I opened this issue now because a comment in #171 made me think about that exact same feature again:

I usually have three or more windows opened in the same workspace, and having to cycle through many of them going only up and down is quite tedious and time wasting (link).

[VuiMuich]

This would be cool! Also would suggest to make it dependant on #318, as it would be most helpful to use this feature with a bind-mode.

Only thing is, that Monocle and MainAndDeck would again need some very special treatment, like instead of showing the window-position-index open a rofi-like list of window indices and respective window titles. But this might even help to improve focus context with floating windows!