message: Increase block size, and set coin base maturity
diff: #include <stdint.h>
  /** The maximum allowed size for a serialized block, in bytes (only for buffer size limits) */
  -static const unsigned int MAX_BLOCK_SERIALIZED_SIZE = 4000000;
  +static const unsigned int MAX_BLOCK_SERIALIZED_SIZE = 8000000;
  /** The maximum allowed weight for a block, see BIP 141 (network rule) */
  -static const unsigned int MAX_BLOCK_WEIGHT = 4000000;
  +static const unsigned int MAX_BLOCK_WEIGHT = 8000000;
  /** The maximum allowed size for a block excluding witness data, in bytes (network rule) */
  -static const unsigned int MAX_BLOCK_BASE_SIZE = 1000000;
  +static const unsigned int MAX_BLOCK_BASE_SIZE = 2000000;
  /** The maximum allowed number of signature check operations in a block (network rule) */
  static const int64_t MAX_BLOCK_SIGOPS_COST = 80000;
  /** Coinbase transaction outputs can only be spent after this number of new blocks (network rule) */
  -static const int COINBASE_MATURITY = 100;
  +static const int COINBASE_MATURITY = 15; //qtum: change to 500 for prod
  /** Flags for nSequence and nLockTime locks */
  enum {
  