Add the ability to select a source image to use in the code.

experimental/webtry/res/css/webtry.css

 body {
   font-family: helvetica arial sans-serif;
   margin: 0;
   padding: 0;
 }
 
 img {
   box-shadow: 2px 2px 5px gray;
   background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAAAAAA6mKC9AAAAAXNSR0IArs4c6QAAAAJiS0dEAP+Hj8y/AAAACXBIWXMAAA7DAAAOwwHHb6hkAAAAB3RJTUUH3gUBEi4DGRAQYgAAAB1JREFUGNNjfMoAAVJQmokBDdBHgPE/lPFsYN0BABdaAwN6tehMAAAAAElFTkSuQmCC");
 }
@@ skipping 62 matching lines @@
     position: absolute;
     top: 3em;
     right: 10px;
     width: 75px;
 }
 
 #tryHistory .tries {
     float: none;
 }
 
+#chooseList {
+  display: flex;
+  flex-flow: row wrap;
+}
+
+#chooseSource {
+  display: none;
+  background: ivory;
+  padding: 1em;
+  border: solid lightgray 2px;
+}
+
+#chooseSource.show {
+  display: block;
+}
+
+#selectedSource {
+  display: none;
+}
+
+#selectedSource.show {
+  display: block;
+}
+
+#sourceCode {
+  display: none;
+}
+
+#sourceCode.show {
+  display: block;
+}
+
 #gitInfo {
     float: right;
     font-size: 70%;
 }
 
 .CodeMirror-lines,
 .CodeMirror-scroll
 {
   background-color: #eee;
 }
 
 .CodeMirror {
   border: solid gray 1px;
 }