reorg, remove old music slice files

app/models/state.ts

@@ -0,0 +1,14 @@
+export interface ById<T> {
+  [id: string]: T
+}
+
+export type OneToMany = ById<string[]>
+
+export interface OrderedById<T> {
+  byId: ById<T>
+  allIds: string[]
+}
+
+export interface PaginatedList {
+  [offset: number]: string[]
+}