A simple way to assign EMV values

As explained on #594.
This allows for mods to assign EMC values in a much simpler way. The old method is still there of course since it's still pretty valid.

I left the logging as TODO because I wasn't sure exactly how I should do it.

Tested with my mods and it worked perfectly. Here's my code example in case you wanna leave it somewhere for people to reference:

```java
private void addEMCValue(Object obj, float value) {
		NBTTagCompound data = new NBTTagCompound();

		data.setFloat("emcValue", value);

		if (obj instanceof ItemStack) {
			NBTTagCompound stackCompound = new NBTTagCompound();
			((ItemStack) obj).writeToNBT(stackCompound);
			data.setCompoundTag("itemStack", stackCompound);
		} else if (obj instanceof String)
			data.setString("oreName", (String) obj);

		FMLInterModComms.sendMessage(getModID(), "emc-simple-assign-value-pre", data);
	}
```