Fixes to large_tank_control computers

Fixed a bug where large_tank_control computers would disassemble into regular general_air_control computers.
Added circuits for large_tank_control computers.
 - large_tank_control circuits can be built in RnD

Created a workaround for unary vents not setting their direction when their id is manually linked
 - When an output's power is toggled, the vent will be set to siphon.

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![atmos_tanks_rebuildable](https://cloud.githubusercontent.com/assets/7979028/3392002/0c9aedce-fcb0-11e3-8ec0-1ce3a34a4476.png)

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Remaining bugs:
 - Newly made general_air_control computers will not load the sensor_information for their linked sensors
 - large_tank_control computers will not link a vent using the multitool's device buffer method
I think most of this is handled in /obj/machinery/computer, just need to change the circuit type to /obj/item/weapon/circuitboard/large_tank_control