Partially refactored server/txpool/block manager/block chain

The Ethereum structure now complies to a EthManager interface which is
being used by the tx pool, block manager and block chain in order to
gain access to each other. It's become simpeler.
TODO: BlockManager => StateManager

ethutil/value.go

@@ -224,3 +224,32 @@ func (val *Value) Append(v interface{}) *Value {
 
 	return val
 }
+
+type ValueIterator struct {
+	value        *Value
+	currentValue *Value
+	idx          int
+}
+
+func (val *Value) NewIterator() *ValueIterator {
+	return &ValueIterator{value: val}
+}
+
+func (it *ValueIterator) Next() bool {
+	if it.idx >= it.value.Len() {
+		return false
+	}
+
+	it.currentValue = it.value.Get(it.idx)
+	it.idx++
+
+	return true
+}
+
+func (it *ValueIterator) Value() *Value {
+	return it.currentValue
+}
+
+func (it *ValueIterator) Idx() int {
+	return it.idx
+}