WP Maps <= 4.9.1 - Unauthenticated SQL Injection via 'location_id' Parameter

The WP Maps plugin for WordPress is vulnerable to time-based blind SQL Injection via the 'location_id' parameter in all versions up to, and including, 4.9.1. This is due to the plugin's database abstraction layer (`FlipperCode_Model_Base::is_column()`) treating user input wrapped in backticks as column names, bypassing the `esc_sql()` escaping function. Additionally, the `wpgmp_ajax_call` AJAX handler (registered for unauthenticated users via `wp_ajax_nopriv`) allows calling arbitrary class methods including `wpgmp_return_final_capability`, which passes the unsanitized `location_id` GET parameter directly to a database query. This makes it possible for unauthenticated attackers to append additional SQL queries into already existing queries that can be used to extract sensitive information from the database.