[added] Trap Block can be placed in Sandbox mode

[mugg91]

Status

• READY: this PR is (to the best of your knowledge) ready to be incorporated into the game.

Description

[added] Trap block to Sandbox builder blocks

Fixes #1983

This PR changes CommonBuilderBlocks.as to make trap blocks placable once again, but only in Sandbox.
There was one free slot available on the first page of builder's block inventory, so it fits perfectly.
This might raise interest in someday adding it back to other gamemodes.

[Vam-Jam]

Works fine from testing (aside from trap block being kinda weird with its collision code)