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/views/helpers.js

@@ -349,16 +349,12 @@ function blockscoutOffTokenNoteHtml(token, chainId) {
     );
 }
 
-// The symbol shown for a token line, from these sources in order:
-//
-// - the bundled list
-// - the tokens the user tracks
-// - the explorer's report, while "Use Blockscout" is on
-//
-// The network is the one with `chainId`, or the active network when none is
-// given. The amount line's scale comes from the same sources. Null when no
-// source names one, so the token lines keep saying `Unknown token` for a token
-// nothing knows.
+// The symbol shown for a token line on the network with `chainId`, or on the
+// active network when none is given: from the bundled list, the tokens the
+// user tracks, and, while "Use Blockscout" is on, the explorer's report. The
+// amount line's scale comes from the same sources. Null when no source names
+// one, so the token lines keep saying `Unknown token` for a token nothing
+// knows.
 function tokenLabel(address, chainId) {
     return resolveTokenSymbol(address, tokenSourcesByChainId(chainId));
 }

src/popup/views/settings.js

@@ -293,8 +293,8 @@ function setUseBlockscout(on) {
 
 // Draws the page again after a network switch, or after another page changed
 // "Use Blockscout" or "Check recipients on Etherscan". Every screen counts as
-// not yet rendered, so "Back" renders again any screen a reopened popup can
-// render. Settings on top is brought up to date in place; any other screen is
+// not yet rendered, so "Back" renders the one it lands on under the new
+// settings. Settings on top is brought up to date in place; any other screen is
 // drawn again as a reopened popup draws it, which is Home for one that cannot
 // be rendered from saved state. Without a wallet any other screen is Welcome or
 // AddWallet. Back only unhides Welcome, so its two checkboxes are set here.