Forced RUST_BACKTRACE=1

Fixed (?) AI crashes #239

• Fixed unit unloading
• Fixed issues with buildings disappearing because of smoke
• Forbade chaining of attached units

• Added wreckage system (#247)
• Added towing system (#161)
• Added a proper FoW layer for air units
• Fixed destruction of transporters with passengers
• More bugfixes)

small bugfixes for gui, roads and helicopters

Initial release