Add Grass to MCX207 (Advanced Bridge)

[Zomon333]

I feel Grass should be added to the list of acceptable blocks for use with the MCX207 sign; Also known as "Advanced Bridge".

I understand this offers the potential to just grow grass and piston it into the range of the sign for a silk-touch effect, but on the opposite end of the spectrum the current setup disallows dirt doors to be hidden in grounds without grass overgrowing and breaking them.

Furthermore, this addition would allow for very amazing builds hidden discretely in the ground for privacy or just a "wow" factor of having something completely, 100% hidden.

Also an irrelevant side note: If someone is determined enough to build a machine to silk touch grass for them because they can't just make a silk touch shovel, they've probably more than done their work. Building a grass generator would require just as many, if not more materials than a shovel, but no XP requirement and it wouldn't exactly break like a shovel either. (Building a circuit of pistons that push grown grass is probably expensive enough to outweigh the value of a silk touch shovel for at least a short while. Grass isn't too expensive of a block, anyways.)