Started using OneLogin SAML lib directly

- Aligned and formatted config options.
- Provided way to override onelogin lib options if required.
- Added endpoints in core bookstack routes.
- Provided way to debug details provided by idp and formatted by
bookstack.
- Started on test work
- Handled case of email address already in use.

app/Exceptions/JsonDebugException.php

@@ -0,0 +1,25 @@
+<?php namespace BookStack\Exceptions;
+
+use Exception;
+
+class JsonDebugException extends Exception
+{
+
+    protected $data;
+
+    /**
+     * JsonDebugException constructor.
+     */
+    public function __construct($data)
+    {
+        $this->data = $data;
+    }
+
+    /**
+     * Covert this exception into a response.
+     */
+    public function render()
+    {
+        return response()->json($this->data);
+    }
+}