style: Minor Beta UI fixes (#1197)

* style(Header): hide scrollbar but still allow side scroll/swipe/drag/touch

* feat: make menu buttons flexiblewith min-width, delete passed in classes, add pointer-cursor

* refactor: use conditional for visibility of plugins settings

* fix: make advanced settings popover appear over nav

* refactor(textarea): minor padding restyling, add max height

* style: make menuItem checkmark invisible instead of hidden so it takes up width space

* style: make presetsMenu trigger an icon button, remove max-width of presets except in mobile view

* style: improve advanced settings mobile styling

* feat: newchat and convo items toggle nav on small screens

* style: improve no presets view

* style: make sure toggle hover effect does not apply on smaller screens

client/src/mobile.css

@@ -111,3 +111,13 @@
     visibility: hidden;
   }
 }
+
+.hide-scrollbar {
+  /* Hide scrollbar for Chrome, Safari, and Opera */
+  scrollbar-width: none; /* For Firefox */
+  -ms-overflow-style: none; /* For Internet Explorer and Edge */
+}
+
+.hide-scrollbar::-webkit-scrollbar {
+  display: none; /* For WebKit browsers */
+}