Make pressure plate texturing more flexible, improve appearance of existing textures

mesecons_pressureplates/init.lua

...cons_textures/textures/jeija_pressure_plate_stone_inv.png

...cons_textures/textures/jeija_pressure_plate_stone_off.png

...extures/textures/jeija_pressure_plate_stone_off_edges.png

mesecons_textures/textures/jeija_pressure_plate_stone_on.png

...textures/textures/jeija_pressure_plate_stone_on_edges.png

...ns_textures/textures/jeija_pressure_plate_stone_wield.png

mesecons_textures/textures/jeija_pressure_plate_wood_inv.png

mesecons_textures/textures/jeija_pressure_plate_wood_off.png

...textures/textures/jeija_pressure_plate_wood_off_edges.png

mesecons_textures/textures/jeija_pressure_plate_wood_on.png

..._textures/textures/jeija_pressure_plate_wood_on_edges.png

...ons_textures/textures/jeija_pressure_plate_wood_wield.png