Rename `app/` to `homepage/` (#974)

Now that we've moved the explorer out of app, it is more concisely
described as the homepage.

Test plan: Rename only. Run `yarn test`.

config/env.js

@@ -6,7 +6,7 @@ const path = require("path");
 
 const paths = require("./paths");
 
-/*:: import type {GitState} from "../src/app/version"; */
+/*:: import type {GitState} from "../src/homepage/version"; */
 
 // Make sure that including paths.js after env.js will read .env variables.
 delete require.cache[require.resolve("./paths")];

src/cli/sourcecred.js

@@ -3,7 +3,7 @@
 
 import type {Command} from "./command";
 
-import {VERSION_SHORT} from "../app/version";
+import {VERSION_SHORT} from "../homepage/version";
 
 import help from "./help";
 import load from "./load";

src/homepage/routeData.test.js

@@ -2,7 +2,7 @@
 
 import {routeData} from "./routeData";
 
-describe("app/routeData", () => {
+describe("homepage/routeData", () => {
   /*
    * React Router doesn't support relative paths. I'm not sure exactly
    * what a path without a leading slash would do; it's asking for

src/homepage/version.test.js

@@ -9,7 +9,7 @@ import {
   parseGitState,
 } from "./version";
 
-describe("app/version", () => {
+describe("homepage/version", () => {
   const version = (): VersionInfo => ({
     major: 3,
     minor: 13,