Mid-Travel Drive-By Damage

On a certain difficulty level, fleets should start to engage each other mid-travel, without invoking the battle tactics pop-up. Fleets should deal a certain percentage of their damage on each other if they are passing by each other on an inter-system line. Maybe even damage passing fleets as they travel through a system with defenders or orbiting fleets. This'll bar "explore-and-retreat" exploitation, hopefully early enough into the game, so that factions don't gain a map advantage too easily. This will also help in the late-game, with system harassment from mobility-focused ships being penalized better.