Dragonlock compatible blocking clip (blocks hill_side parts from falling downwards)

This clip is like a mirror version of the original Core_Shim. It prevents side parts from falling down and gives mountain structures increased durability.

What it helps with:

1. your mountain sides don‘t slide down anymore.

2. You don‘t need a blocking clip for every mountain core because the ones next to it also block cores from sliding down. That saves you a few tiles every mountain structure.

3. Since the blocking bottom hexes also seem to give the whole structure more rigidity si