Save placed blocks to prevent counting them in the block objective

[Wolf2323]

The block objective currently does also count blocks placed by other people. This cause people to work together to complete the objective.

To solve this issue we could save all blocks placed by players. But we also need to respect blocks moved by piston and co.
A possible solution could be https://github.com/mfnalex/CustomBlockData

If we solve this by saving all the blocks, we may have issues on server, that use regions that regenerate the blocks, or other mechanics that do not fit the normal MC behaviour.
If this is solved, we can solve this issue.