Add wall version of beta brick terrain edge

[fidwell]

Resolves #340. Created a new wall object that match the texture of the brick wall beta terrain edge.

[ZeeMaji]

I'm a bit unsure if it would make sense to include the rock walls as there's no wall version of the final/RCT2 rock edge.

For the names i would just shorten them to "Brick Wall" and "Rock Wall" or even just "Wall" as the wall names in vanilla are pretty generic.

For the object ids should remain "official" as they were not a part of the rct1 beta, they're just official additions based on the beta assets.

[fidwell]

I didn't even consider that some of the terrain edges don't have corresponding walls. I probably wouldn't have made the rock wall if I'd thought about it.

If anyone feels strongly about not having them, that's fine by me.

[tbarford]

Maybe add that wall texture as a scenery wall, too?

[deurklink]

I think it would be really nice to have the other wall edge textures as scenery too

[Gymnasiast]

I generally want to keep the brakes on adding too much extra content. Could you put forth your arguments for including these as official content?

[fidwell]

Having the beta brick wall would create a nice parity with how the existing brick terrain edge has a wall that goes with it.

The rock wall doesn't fit as well and I don't have any strong arguments about keeping that one.

[karst]

I could see the brick wall fit in with the default objects, I could see rock wall (as well as for the non-beta versions) be a non-essential official object.
@Gymnasiast good ideas for the object store, too?

[ZeeMaji]

For what it's worth, the brick wall was the only one i mentioned on the issue that prompted this PR. #340.

[fidwell]

I've rebased this PR and limited the change to just adding the brick wall.