Liquid Element Sensor can't be build

There is no liquid element sensor in the game.

LogicElementSensorLiquidConfig is included in the source code, but it's not added to the build menu. Reading a request for "liquid version of the gas element sensor" on the forum, I figured I would just try it and see what happens. Turns out it's mostly implemented and only needs a few changes:

1. BuildingDef needs Floodable to be set to false (a flooded liquid sensor doesn't make sense)
2. Lacks graphics (uses hydro sensor as placeholder)
3. Should be added to the tech tree (I propose adding to GenericSensors)

Other than that it seems to work just fine. Since it's both requested and practically done (except graphics), it should be considered for the Launch.

I released a mod adding this sensor, but it really is just a copy paste of LogicElementSensorLiquidConfig, but with different class name and ID. I decided on this approach instead of just enabling the existing building because I want to make sure it won't conflict with future ONI patches.