Create indoors house tileset

[Diarandor]

• [x] Ground tiles (several variants)
• [x] Walls
• [x] Carpets
• [x] Decoration: table, chair, bookshelf
• [x] Chimney (fireplace), table lamp
• [x] Cats!!! :3
• [x] Ceilings
• [x] Windows
• [x] Doors
• [x] New wall colors: "red" (rename current red to "orange"), "gray" (use a better color), "darkblue", "violet", "purple", "darkgreen", etc.
• [x] Low wall borders
• [ ] Pillars
• [ ] Spiral stairs
• [x] Stairs (straight stairs to the same map)
• [x] Semitransparent "darkening" tiles (for customization of colors)
• [x] More floor tiles, and define (give pattern names to) the remaining ones

More stuff:

• [ ] Wall variants with different style (?). (Not prioritary)
• [ ] Ice ceilings for Kaleido's home too (compatible with blue walls).

[Diarandor]

@christopho Do we need doors in the tileset? Or should we better add them as entities?