Service provider and other cleanup

- Removed old 'exposeTranslations' system to instead use new component
 option system.
- Extracted validation rules into their own service provider.
- Cleaned up some formatting/comments in the repos.

app/Providers/CustomValidationServiceProvider.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace BookStack\Providers;
+
+use Illuminate\Support\Facades\Validator;
+use Illuminate\Support\ServiceProvider;
+
+class CustomValidationServiceProvider extends ServiceProvider
+{
+
+    /**
+     * Register our custom validation rules when the application boots.
+     */
+    public function boot(): void
+    {
+        Validator::extend('image_extension', function ($attribute, $value, $parameters, $validator) {
+            $validImageExtensions = ['png', 'jpg', 'jpeg', 'gif', 'webp'];
+            return in_array(strtolower($value->getClientOriginalExtension()), $validImageExtensions);
+        });
+
+        Validator::extend('no_double_extension', function ($attribute, $value, $parameters, $validator) {
+            $uploadName = $value->getClientOriginalName();
+            return substr_count($uploadName, '.') < 2;
+        });
+
+        Validator::extend('safe_url', function ($attribute, $value, $parameters, $validator) {
+            $cleanLinkName = strtolower(trim($value));
+            $isJs = strpos($cleanLinkName, 'javascript:') === 0;
+            $isData = strpos($cleanLinkName, 'data:') === 0;
+            return !$isJs && !$isData;
+        });
+    }
+}