Truncate addresses by 2 chars to compensate for color dot width

Move truncateMiddle to helpers.js for reuse. Shorten displayed addresses
by 2 characters wherever a dot is shown: home view (40 char max), tx list
(maxAddr - 2), and address detail container (40ch width).

src/popup/views/home.js

@@ -4,6 +4,7 @@ const {
     showFlash,
     balanceLinesForAddress,
     addressDotHtml,
+    truncateMiddle,
 } = require("./helpers");
 const { state, saveState } = require("../../shared/state");
 const { deriveAddressFromXpub } = require("../../shared/wallet");
@@ -47,7 +48,7 @@ function render(ctx) {
             }
             const addrUsd = formatUsd(getAddressValueUsd(addr));
             html += `<div class="flex text-xs">`;
-            html += `<span class="flex items-center" style="width:42ch;max-width:100%">${addr.ensName ? "" : dot}${addr.address}</span>`;
+            html += `<span class="flex items-center" style="width:42ch;max-width:100%">${addr.ensName ? "" : dot}${truncateMiddle(addr.address, 40)}</span>`;
             html += `<span class="text-right text-muted flex-1">${addrUsd}</span>`;
             html += `</div>`;
             html += balanceLinesForAddress(addr);