gui/liquids should reset temperature when clearing magma

[myk002]

[Bumber64]

It seems that it does clear temperature on the tiles you select. What it doesn't do is clear the flow_forbid designation when in magma removing mode. (It correctly does so if you use water removal to remove magma.) It doesn't clear temperature of adjacent tiles, which you can get around by clearing a larger area. We should probably do a proper calculation based on remaining adjacent magma instead of always setting to 10015 U (A Maps module fn for that might be desired).

Another issue is that removing 1 magma from 7/7 water results in 6/7 magma.