Add initial graph data types (#34)

backend/graph.js

@@ -0,0 +1,26 @@
+// @flow
+
+export type ID = {
+  pluginName: string,
+  repositoryName: string,
+  name: string,
+};
+
+export type GraphNode<T> = {
+  id: ID,
+  edges: ID[],
+  payload: T,
+};
+
+export type GraphEdge<T> = {
+  id: ID,
+  sourceId: ID,
+  destId: ID,
+  weight: number,
+  payload: T,
+};
+
+export type Graph = {
+  nodes: {[stringID: string]: GraphNode<mixed>},
+  edges: {[stringID: string]: GraphEdge<mixed>},
+};