fix: a popup that opened on Welcome keeps refreshing once the first wallet is added (closes #530)

The ten-second refresh was started only by init(), and only when a wallet
existed as the popup opened, so a popup that opened on Welcome refreshed the
new wallet once and then showed that balance until it was reopened. init()
and the three import paths on AddWallet now call startRefresh(), which
refreshes at once and starts the ten-second refresh unless it is already
running, and does nothing while the recovery screen is up. The two AddWallet
tests that build their own context pass it in place of the refresh they
passed before.

Model: opus-5-5

tests/firstWalletRefresh.test.js

@@ -61,12 +61,16 @@ async function importOn(page, { tab, field, secret }) {
     await page.click("btn-add-wallet-confirm");
 }
 
+// Fake timers hold the timer of the flash message an import ends with, which
+// would otherwise fire after cleanupPopup() has removed the page and throw.
 beforeEach(() => {
+    jest.useFakeTimers();
     chainBalance = "0.0";
 });
 
 afterEach(() => {
     cleanupPopup();
+    jest.useRealTimers();
 });
 
 describe("a popup that opened on Welcome", () => {