[#137] sdk: Implement netmap filtering and selection

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/netmap/container.go

@@ -0,0 +1,19 @@
+package netmap
+
+// ContainerNodes represents nodes in the container.
+type ContainerNodes interface {
+	Replicas() []Nodes
+	Flatten() Nodes
+}
+
+type containerNodes []Nodes
+
+// Flatten returns list of all nodes from the container.
+func (c containerNodes) Flatten() Nodes {
+	return flattenNodes(c)
+}
+
+// Replicas return list of container replicas.
+func (c containerNodes) Replicas() []Nodes {
+	return c
+}