Revert "Revert "Add POS Cutoff Block""

This reverts commit 8323619d52af562b1f6ffb539ff7b0cf1e9164cc.
Revert "Revert "Disallow POW blocks after 30K and fix broken POS""

This reverts commit 0971d505f685d11b1f1db7a5bdd4d517ce3e0d68.