Adding serial.set(Rx|Tx)BufferSize (#1931)

* Fix for https://github.com/Microsoft/pxt-microbit/issues/1929

* bump pxt

* updated docs

* fix default values

* moving dialogs to react

* moving to react

* typo

* typo

theme/style.less

@@ -94,3 +94,23 @@
 .ui.downloaddialog.modal>.content {
     padding: 1rem;
 }
+
+.ui.webusbpair, .ui.upload {
+    .firmware {
+        background-color: #FFFFCE;
+        div.image {
+            justify-content: center;
+            display: flex;
+            padding: 1rem;
+    
+            img {
+                height:100px;            
+            }
+        }
+    }
+    .instructions {
+        img {
+            margin-bottom:1rem;            
+        }
+    }
+}