add lgate/rgate for bandit and cobblestone walls
add template rule for windmill blade blocks, flywheel storage blocks.
add windmill control block to list of torque-tiles registered for
regular torque-tile block rule.  Fixes windmills not generating properly
in structure system.
add image for windmill for structure pack
add spawner icons for faction-based npc bard npc-types
clean up handling of ticked structure builder.  Closes #192