Light mode: more fixes & cleanup:

- Remove lots more unused files
- Make light mode toggles for Exchange and Wallet images
- Change layout for exchanges and wallets to work better at some screen
  widths (between mobile and full 1080p)
- Fix light mode styles for some dev tools, carbon calculator, Edit
  button, footer, etc.

styles/_pages.scss

@@ -89,6 +89,30 @@
   }
 }
 
+#wallets {
+  @each $wallet in "ledger", "secalot", "trezor", "xumm", "trust", "gatehub" {
+    #wallet-#{$wallet} {
+      content: url("../img/wallets/#{$wallet}.svg");
+    }
+  }
+}
+
+#top-exchanges {
+  // Vector logos
+  @each $exchange in "bitstamp", "kraken", "cex-io", "liquid", "lmax", "bitfinex", "etoro" {
+    #exch-#{$exchange} {
+      content: url("../img/exchanges/#{$exchange}.svg");
+    }
+  }
+
+  // Raster logos
+  @each $exchange in "bittrex", "currency-com", "ftx" {
+    #exch-#{$exchange} {
+      content: url("../img/exchanges/#{$exchange}.png");
+    }
+  }
+}
+
 // XRPL Overview Page
 #xrpl-overview-purple {
   position: absolute;
@@ -117,6 +141,10 @@
   }
 }
 
+#validator-graphic {
+  content: url(../img/validators.svg);
+}
+
 .page-uses {
   background: url(../img/backgrounds/use-cases-blue.svg) no-repeat;
   background-position-x: left -20vw;
@@ -170,7 +198,7 @@
 }
 .hidden-section {
   overflow: hidden;
-  visibility: none;
+  visibility: hidden;
   height: 0;
   &.show {
     overflow: auto;