feat: Add quick settings menu with theme switcher and other changes (#673)

Co-authored-by: Mo Bitar <mo@standardnotes.org>
Co-authored-by: Antonella Sgarlatta <antsgar@gmail.com>

app/assets/stylesheets/_menus.scss

@@ -17,13 +17,20 @@
   max-height: calc(85vh - 90px);
 }
 
-.sn-account-menu {
+.sn-account-menu,
+.sn-quick-settings-menu {
   z-index: $z-index-footer-bar-item-panel;
   @extend .bottom-100;
   @extend .left-0;
   @extend .cursor-auto;
 }
 
+.sn-menu-border {
+  @extend .border-1;
+  @extend .border-solid;
+  @extend .border-gray-300;
+}
+
 .sn-account-menu-headline {
   @extend .sk-h2;
   @extend .sk-bold;