Actual Shelf Mushrooms

Makes the Shelf Mushroom an actual shelf! This mod adds two new growth stages to the shelf mushroom, allowing you to place blocks on them. 

About

The final growth stage is pushable by pistons, won’t break if the supporting block is destroyed, is pathfindable by mobs, and can hold signs. Other than that, the new growth stages differ only in width and depth and are mostly a matter of taste (i.e., whether you want a gap between them).

They both use the same texture as the (vanilla) large variant of the shelf mushroom, so they'll adapt if you use any texture pack that only targets those two.

No new blocks are added, so if you decide to ever remove this mod, the shelf mushrooms will just return to their first growth stage.