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 where they are made. 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 naming the setting. After either changes in
Settings, Back draws again any screen a reopened popup can draw. ENS lookups
ask only the RPC endpoint, so a name resolved off-chain does not resolve.
README and the user guide say what is contacted by default and what each
setting adds.

Model: opus-5-5

tests/confirmTxNetworkSwitch.test.js

@@ -142,13 +142,19 @@ jest.mock("../src/popup/views/txStatus", () => ({
 }));
 
 // The Etherscan label check is its only caller here: the explorer pages it
-// asks for are recorded, and nothing is fetched.
+// asks for are recorded, and nothing is fetched. The stored profile has the
+// check turned on.
 global.fetch = jest.fn(() => {
     throw new Error("tests must not perform network requests");
 });
 
 const { makeStorageStub } = require("./support/storageStub");
-global.chrome = { storage: makeStorageStub(), runtime: { sendMessage() {} } };
+global.chrome = {
+    storage: makeStorageStub({
+        autistmask: { checkRecipientsOnEtherscan: true },
+    }),
+    runtime: { sendMessage() {} },
+};
 
 // A stub DOM: every id resolves to a recording element.
 const elements = new Map();