[index] Improve error handling (#555)

Add additional information to error message:

- Name of the bridge
- Possible solutions
- Error description
- Error code
- Error message

* Output type changed from 'text' to 'html'
* Added styles for the error page
* Added a button to remotely open a GitHub issue

Closes #525

static/style.css

@@ -244,3 +244,37 @@ h5 {
 	display: block;
 
 }
+
+/* Additional styles for error pages */
+
+.exception-message {
+
+	background-color: #c00000;
+	color: #FFFFFF;
+
+	font-weight: bold;
+
+	box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.3);
+	border-radius: 2px;
+	border: 1px solid transparent;
+
+	width: 80%;
+	margin: auto;
+	margin-bottom: 6px;
+
+}
+
+.advice {
+
+	margin-left: auto;
+	margin-right: auto;
+
+	display: table;
+
+}
+
+.advice > li {
+
+	text-align: left;
+
+}