implement montblanc hard fork

[jed-wemade]

After the block reached to mont blanc fork, mining worker skips committing work for the futher mont blanc blocks.
Instead, warning log appears constantly:

WARN [09-24|01:21:30.277] go-wemix skips mining due to mont blanc fork height=30 parent-hash=11cc16..c0ea5f
WARN [09-24|01:21:31.277] go-wemix skips mining due to mont blanc fork height=30 parent-hash=11cc16..c0ea5f

In addition, mont blanc block excluding the block generated at fork time is filtered out during header verification.

DEBUG[09-25|10:07:14.819] Propagated block verification failed     peer=72c3d5b3a6972776253f2e535dcb52199e6fbf58cce653bcb80eab965e97e2ce number=10,867,700 hash=17583b..92886c err="go-wemix does not support mont blanc fork"
DEBUG[09-25|10:07:14.819] Message handling failed in `eth`         id=72c3d5b3a6972776 conn=staticdial err=EOF
DEBUG[09-25|10:07:14.819] Removing Ethereum peer                   peer=72c3d5b3 snap=true
DEBUG[09-25|10:07:14.819] Message handling failed in `snap`        peer=72c3d5b3 err=EOF
DEBUG[09-25|10:07:14.819] Removing p2p peer                        peercount=1 id=72c3d5b3a6972776 duration=32.627s     req=false err="useless peer"

[egonspace]

LGTM

[egonspace]

This merge was reset because it had not been done by squash and merge