allow display of arbitrary data in advanced display boards

[Waoweens]

Is your feature request related to a problem? Please describe.
the advanced display boards are really cool, but they can only be used to display train-related data. right now when i link it to a display link and put that display link on something other than a train station, the board will display nothing (or "out of service" or "time: XX:XX")

Describe the solution you'd like
a new display type for arbitrary data from a display link.

and also maybe integration with certain other contraptions, such as displaying the current floor when attached to an elevator pulley contraption.

Describe alternatives you've considered
-

Additional context
this is what happens currently:

"platform display" type is selected here