[FEAT] Show marker for items that end up on belts

[VladimirSporynin]

Is your feature request related to a problem? Please describe.
It can be difficult at times to keep in mind exactly what items end up on certain belt lines.

Describe the solution you'd like
Markers on the belt line would help visualize item outputs. Markers would be displayed when an inserter or other belts would be placing items on the belt. Rotating an inserter or a belt away or destroying it would remove the markers. Items would be displayed on their respective belt sides and markers would be shown for up to three different items per side. Any more are represented by a + symbol. Items are only displayed after the related inserter or belt.

Describe alternatives you've considered
Alternatively, items could only be shown as a single marker at the end of a belt line.

Additional context
Here is an image of what it might look like. For the main solution the image should have the pipe along the entire belt line starting at the inserter.

This issue is related to a few other existing issues:
Related to #22
Related to #221
This feature is the first step towards feature #21.