core: reduce max allowed queued txs per address

Transactions in the queue are now capped to a maximum of 200
transactions. This number is completely arbitrary.

common/types.go

@@ -1,6 +1,7 @@
 package common
 
 import (
+	"fmt"
 	"math/big"
 	"math/rand"
 	"reflect"
@@ -95,3 +96,13 @@ func (a *Address) Set(other Address) {
 		a[i] = v
 	}
 }
+
+// PP Pretty Prints a byte slice in the following format:
+// 	hex(value[:4])...(hex[len(value)-4:])
+func PP(value []byte) string {
+	if len(value) <= 8 {
+		return Bytes2Hex(value)
+	}
+
+	return fmt.Sprintf("%x...%x", value[:4], value[len(value)-4])
+}