Added configurable API throttling, Handled API errors standardly

app/Http/Middleware/ThrottleApiRequests.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace BookStack\Http\Middleware;
+
+use Illuminate\Routing\Middleware\ThrottleRequests as Middleware;
+
+class ThrottleApiRequests extends Middleware
+{
+
+    /**
+     * Resolve the number of attempts if the user is authenticated or not.
+     */
+    protected function resolveMaxAttempts($request, $maxAttempts)
+    {
+        return (int) config('api.requests_per_minute');
+    }
+
+}