Add address color dots and cached ENS reverse lookups

Deterministic colored dots derived from address bytes (16-color palette)
displayed before every address. ENS reverse resolution for transaction
counterparties with 12-hour localStorage cache.

src/popup/views/helpers.js

@@ -99,6 +99,35 @@ function balanceLinesForAddress(addr) {
     return html;
 }
 
+const ADDRESS_COLORS = [
+    "#e6194b",
+    "#3cb44b",
+    "#4363d8",
+    "#f58231",
+    "#911eb4",
+    "#42d4f4",
+    "#f032e6",
+    "#bfef45",
+    "#fabed4",
+    "#469990",
+    "#dcbeff",
+    "#9a6324",
+    "#800000",
+    "#aaffc3",
+    "#808000",
+    "#000075",
+];
+
+function addressColor(address) {
+    const idx = parseInt(address.slice(2, 6), 16) % 16;
+    return ADDRESS_COLORS[idx];
+}
+
+function addressDotHtml(address) {
+    const color = addressColor(address);
+    return `<span style="width:8px;height:8px;border-radius:50%;display:inline-block;background:${color};margin-right:4px;vertical-align:middle;flex-shrink:0;"></span>`;
+}
+
 module.exports = {
     $,
     showError,
@@ -106,4 +135,6 @@ module.exports = {
     showView,
     showFlash,
     balanceLinesForAddress,
+    addressColor,
+    addressDotHtml,
 };