More love :D

* Improved all the code.
* Improved the notifications. Now the emails are sent with the WooCommerce email template.
* Improved the plugin settings. Removed some options in favor of the WooCommerce mailer.
* Entered the woocommerce_review_reminder_email_subject filter for change the email subject.
* Entered the woocommerce_review_reminder_email_title filter for change the email title.
* Entered the woocommerce_review_reminder_email_message filter for change the email message.
* Added screenshots
* Improved the readme.txt