webrepl.html: Add warning on accessing over HTTPS.

Per web content policy, accessing page over HTTPS requires it to use wss:
for WebSocket access, but we don't support SSL WebSockets for WebREPL.

Author: mcauser

webrepl.html

@@ -106,13 +106,28 @@
         cursorBlink: false
       });
       term.open(document.getElementById("term"));
+      show_https_warning();
     };
     window.addEventListener('resize', function() {
         var size = calculate_size(self);
         term.resize(size[0], size[1]);
     });
 }).call(this);
 
+function show_https_warning() {
+    if (window.location.protocol == 'https:') {
+        var warningDiv = document.createElement('div');
+        warningDiv.style.cssText = 'background:#f99;padding:5px;margin-bottom:10px;line-height:1.5em;text-align:center';
+        warningDiv.innerHTML = [
+            'At this time, the WebREPL client cannot be accessed over HTTPS connections.',
+            'Use a HTTP connection, eg. <a href="http://micropython.org/webrepl/">http://micropython.org/webrepl/</a>.',
+            'Alternatively, download the files from <a href="https://github.com/micropython/webrepl">GitHub</a> and run them locally.'
+        ].join('<br>');
+        document.body.insertBefore(warningDiv, document.body.childNodes[0]);
+        term.resize(term.cols, term.rows - 7);
+    }
+}
+
 function button_click() {
     if (connected) {
         ws.close();