Added MJML/HTML codeeditor with a preview for template design.

client/src/lib/sandbox-common.scss

@@ -0,0 +1,71 @@
+$navbarHeight: 34px;
+$editorNormalHeight: 800px !default;
+
+.editor {
+  .host {
+    @if $editorNormalHeight {
+      height: $editorNormalHeight;
+    }
+  }
+}
+
+.editorFullscreen {
+  position: fixed;
+  top: 0px;
+  bottom: 0px;
+  left: 0px;
+  right: 0px;
+  z-index: 1000;
+  background: white;
+  margin-top: $navbarHeight;
+
+  .navbar {
+    margin-top: -$navbarHeight;
+  }
+
+  .host {
+    height: 100%;
+  }
+}
+
+.navbar {
+  background: #DE4320;
+  width: 100%;
+  height: $navbarHeight;
+}
+
+.logo {
+  float: left;
+  height: $navbarHeight;
+  padding: 5px 0 5px 10px;
+  filter: brightness(0) invert(1);
+}
+
+.title {
+  padding: 5px 0 5px 10px;
+  font-size: 18px;
+  font-family: sans-serif;
+  font-family: "Ubuntu",Tahoma,"Helvetica Neue",Helvetica,Arial,sans-serif;
+  font-weight: bold;
+  float: left;
+  color: white;
+  height: $navbarHeight;
+}
+
+.btn {
+  display: block;
+  float: right;
+  padding: 0px 15px;
+  line-height: $navbarHeight;
+  text-align: center;
+  color: white;
+  font-size: 14px;
+  font-weight: bold;
+  font-family: sans-serif;
+  cursor: pointer;
+}
+
+.btn:hover {
+  background-color: #b1381e;
+  color: white;
+}