Concrete Wall Block 1.2

I improved the jbeam greatly so that we can actually build things with it.
Pile them up and use the usual "attach nodes" feature to attach them together to make something strong.

I added nodes and beams to:

- fix sinking through one another
- increase mass and inertia
- have more control to place it more accurately
- have more attachment points

Known issues:

- the block can be prone to small vibrations when in contact with other blocks. You can eliminate this by moving it around a little...

The jbeam from the original BeamNG Concrete Retaining Wall does not fit perfectly the dimensions of the blocks.
I fixed that in this update.