Room editor improvements

[NyakoFox]

This PR adds a few improvements for the room editor.

• The grid now has independent width and height.
• The grid is now automatically set to what most tiles are sized, instead of being a hardcoded 16.
• Adding objects to rooms by dragging and dropping now places them at the correct position.
• You can now "paint" objects and tiles by holding down ALT and clicking and dragging.
• Tile selection has been remade, where you now click on a tile to select it instead of dragging around the red rectangle.
• Resizing the tile selection rectangle can now go to the left and up.