Shroomlight rename to Moltshroom

Moltshroom! A new name for the Shroomlight light source block we are getting in the nether update! 

The idea behind this rename is that it is keeping close to the Minecraft style. The Shroomlight name is quite different from most blocks, especially naturally generated ones. Moltshroom, as an alternative to it, is closer fitting in style as it sounds like something natural. It has "Molt" like molten, a very nethery feel which also infers glowing or light-giving properties and the staple "shroom". 

Let's see if this gets anywhere!