Added new models of rocks. A new stylized textures for this.

The asset contains quality lowpoly models of ruins, magic crystal, any bricks, columns and rocks. Stone diffuse textures are made in a stylized genre and optimized for mobile shaders. Normal maps are used to underline the relief, gloss map is used for gloss in the alpha diffuse channel.

The asset also uses a hand-drawn leaf texture to create simple top/down vegetation.