Add ability to place arbitrary material spatters on map

[quietust]

In order to make subterranean stone tiles farmable, they need to be made muddy. Currently, the only way to do this is to use the liquids tool to place water in an adjacent tile and hope it spreads into the tiles you want - it would be much more convenient to have a way to directly place mud on the map.

This shouldn't be constrainted to only placing mud - ideally, it should allow placing any material in any valid state (e.g. MUD + SOLID for mud, WATER + POWDER for snow, CREATURE_MAT:DWARF:BLOOD + LIQUID for liquid dwarf blood, and possibly even CREATURE_MAT:FORGOTTEN_BEAST_N:POISON + LIQUID for beast venom). Invalid material states should be disallowed, whether by checking the MELTING_POINT/BOILING_POINT or by checking for an absence of state names (or both).

This could be done either as a command-line tool placing the contaminant in the tile beneath the keyboard cursor, or it could be a graphical tool where you select the material+state from a menu and then use the mouse to paint the spatter onto the map (either by placing individual rectangles or potentially click-and-drag).

Each tile's temperature could potentially be used to automatically select the material's state, reducing the choice to just SOLID, POWDER, and PASTE.

This tool should mimic the exact behavior of the in-game function worldst::add_material_spatter_tile (which can be provided upon request).

[Bumber64]

It's probably good to have a command-line option behind the GUI. That way you could have liquids and gui/liquids automatically invoke the command to place mud under the water.