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 and each
recipient to Etherscan. 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. Each gated request reads its setting from storage
before it asks and when the answer lands, and drops a late answer. An open popup
takes another page's change and draws its screens again. While "Use Blockscout"
is off, no address keeps an untracked token, and no screen names a token from
Blockscout's report. ENS lookups ask only the RPC endpoint.

Model: opus-5-5

src/popup/viewRouter.js

@@ -38,11 +38,16 @@ function markViewRendered(view) {
     if (view) renderedViews.add(view);
 }
 
-// Begin a fresh page-load scope. The popup gets one by being loaded, and
-// asks for one after a network switch, because every screen then on the page
-// shows the previous network (showNewNetwork() in views/settings.js); the
-// unit tests, which simulate several page loads against one module
-// instance, ask for one too.
+// Begin a fresh page-load scope. The popup gets one by being loaded. It also
+// asks for one when every screen on the page is out of date:
+//
+//   - after a network switch, since those screens show the previous network
+//     (showNewSettings() in views/settings.js)
+//   - after "Use Blockscout" or "Check recipients on Etherscan" changes, here
+//     or on another page, since those screens were drawn under the old setting
+//
+// The unit tests ask for one too. They simulate several page loads against one
+// module instance.
 function resetRenderedViews() {
     renderedViews.clear();
 }