Update last of existing services to use repositories, includes unit tests

Also update PHPDocs on all the repository interfaces and classes to be correct.

app/Contracts/Repository/DatabaseHostInterface.php

@@ -26,5 +26,14 @@ namespace Pterodactyl\Contracts\Repository;
 
 interface DatabaseHostInterface extends RepositoryInterface
 {
+    /**
+     * Delete a database host from the DB if there are no databases using it.
+     *
+     * @param  int $id
+     * @return bool|null
+     *
+     * @throws \Pterodactyl\Exceptions\DisplayException
+     * @throws \Pterodactyl\Exceptions\Repository\RecordNotFoundException
+     */
     public function deleteIfNoDatabases($id);
 }