YITH Booking and Appointment for WooCommerce Premium 5.18.0

* New: support for WooCommerce 3.9
* New: integration with YITH WooCommerce Review Reminder
* New: send 'Cancelled Booking' email to customers when the booking is cancelled by the customer
* New: when searching for booking products with Booking Search Forms on Shop page, prices reflect the selected parameters (dates, people and services)
* New: search forms autofilled after searching
* Update: language files
* Fix: integration with YITH WooCommerce Deposits and Down Payments
* Fix: issue with non-numeric values
* Fix: issues with custom extra cost when used with WPML
* Fix: issue with search form widget when using WP Customizer
* Fix: wrong "from" and "to" fields in request a quote table
* Fix: issue when emptying booking categories field
* Fix: init plus and minus in people select box
* Tweak: improved style
* Dev: added yith_wcbk_booking_form_after_label_duration action
* Dev: added yith_wcbk_ics_event_summary filter
* Dev: added yith_wcbk_ics_event_description_data filter
* Dev: added yith_wcbk_ics_event_description filter
* Dev: added yith_wcbk_google_calendar_sync_event_args filter
* Dev: added yith_wcbk_searched_value_for_field filter

* Update: plugin framework
* Update: Dutch language

* Fix - next month issue on calendar
* Fix - frontend styles for RTL languages
* Fix - update lookup table when syncing the booking price to avoid issues when sorting and filtering booking products by price
* Update - plugin framework
* Update - language files
* Tweak - fixed people label in search forms
* Tweak - specific CSS class for services in booking_services shortcode
* Dev - new filter 'yith_wcbk_notice_for_request_confirmation_login_required'
* Dev - new filter 'yith_wcbk_button_text_for_request_confirmation_login_required'
* Dev - new filter 'yith_wcbk_apply_weekly_discount' to prevent applying to of quickly discount in combination with monthly discount
* Dev - new filter 'yith_wcbk_ajax_booking_available_times_formatted_time' to let third party code filter time labels
* Dev - new action 'yith_wcbk_after_request_confirmation_action'
* Dev - new filter 'yith_wcbk_redirect_after_request_confirmation_action'