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.
Update main.h
Update main.cpp
Update main.cpp
Update main.cpp
Update main.cpp
Update main.cpp
Update main.h
Update main.cpp
Update main.h
Update main.cpp, add conf
Merge pull request #9 from cryptogears/master

Begin PoS at 17000, end PoW at 17500