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/viewRouter.js

@@ -38,10 +38,15 @@ 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
+// 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+// asks for one when every screen on the page is out of date: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, which simulate several page loads against one module
 // instance, ask for one too.
 function resetRenderedViews() {
     renderedViews.clear();