The Events Calendar Pro 6.4.0

* Feature - Add system to check plugin versions to inform you to update and prevent site breaking errors [116841]
* Tweak - Added filters: `tribe_not_php_version_names`
* Deprecated - Constants REQUIRED_TEC_VERSION in Tribe__Events__Pro__Main, use Plugin Dependency Checking system to check for requirements
* Deprecated - The functions `tribe_init_ecp_addon()` and `Tribe_ECP_Load()` and `register_active_plugin()` method has been deprecated in `Tribe__Events__Pro__Main` in favor of Plugin Dependency Checking system
* Language - 7 new strings added, 51 updated, 0 fuzzied, and 1 obsoleted

* Fix - Recurrence meta box will show again on Classic Editor
* Fix - Update textdomain for strings coming from the Gutenberg extension merge
* Fix - Fixed a number of small layout bugs with the new Twenty Nineteen core theme
* Language - 2 new strings added, 58 updated, 0 fuzzied, and 1 obsoleted

* Fix - Display recurrence section in classic editor for all users that don't have blocks