Allow roboports to report construction requests

[Azcranta]

I really like the feature to read logistics requests as is allows for subnetworks, however it would be very helpful for constructing bases if I could read construction requests directly, rather than relying on reading logistic requests from spidertron/tanks inorder to automate delivery of construction materials to subnets.

I can understand if there are technical limitations due to the way the reading of construction requests are structured, but this would make train based bases with independent roboports more effective.