#113 Implement block signature verification

• [feat] #113 (closed): Handle block signature verification
• [test] #113 (closed): Add test for block signature verification
• [test] #113 (closed): Add test for transaction signature verification
• [mod] Remove useless cotes

changed milestone to %0.56.0

added Crypto D: Block enhancement labels

Reviewed ok. You can merge on dev.

merged

mentioned in issue silkaj#262 (closed)