fix: Blockscout and Etherscan lookups are off until the user turns them on (closes #668)

Out of the box the wallet sent the user's addresses to Blockscout for history
and token lookups. It sent each recipient to Etherscan for its label. Two
settings, "Use Blockscout" and "Check recipients on Etherscan", now gate those
requests. Both are off in a new install and offered unticked on Welcome and in
Settings. While one is off, the screens that relied on it say so in a plain
line. The balance refresh and the Etherscan check read the stored setting. An
open popup takes a change another page saved and draws its screens again. While
"Use Blockscout" is off, no address keeps an untracked token. ENS lookups ask
only the RPC endpoint.

Model: opus-5-5

src/popup/views/settings.js

@@ -393,11 +393,12 @@ function init(_ctx) {
 
     // Each change is made inside the save, holding the lock. Then
     // followStoredSettings() in src/popup/index.js never takes this page's
-    // unsaved change for another page's. The screens under Settings were drawn
-    // under the old setting. So each change makes every screen but Settings count as not yet
-    // drawn, as a network switch does. Back then draws again any screen a
-    // reopened popup can draw. Back only unhides Welcome, so its boxes are set
-    // here too.
+    // unsaved change for another page's.
+    //
+    // The screens under Settings were drawn under the old setting. So each
+    // change makes every screen but Settings count as not yet drawn, as a
+    // network switch does. Back then draws again any screen a reopened popup
+    // can draw. Back only unhides Welcome, so its boxes are set here too.
     $("settings-use-blockscout").addEventListener("change", async () => {
         const on = $("settings-use-blockscout").checked;
         await saveState(() => setUseBlockscout(on));