new feature: contextual grid

this update introduces a new feature: contextual grid

holding down shift will display the grid, which will be positioned relative to the camera angle and 3d cursor

when you paint/delete tiles on the grid, you can do so in one continuous motion, instead of picking them one by one

there is also a change to control scheme: removing tiles is now done by holding down control/command depending on os. this allows to remove them with or without using the grid