Modern Bulk Rail Loaders: Pooled (Unofficial 2.1 Fix)

Unofficial Factorio 2.1 port of Modern Bulk Rail Loaders: Pooled, renamed so it can coexist on the portal with the original. Original mod by Sølve Monteiro (https://github.com/solvemon/bulk-rail-loaders-pooled); 2.1 fix by kfsone. Bulk train loading/unloading silos that share a single pooled inventory per station. Contents can never get unbalanced between wagons, so automated deliveries (e.g. Cybersyn) always complete when the station total suffices. Pooled-architecture rework inspired by Modern Bulk Rail Loader by Vyl. Replaces the original mod: disable/remove modern-bulk-rail-loader-pooled; silos and pools already in a save are re-registered on first load.