Gravity Perks - Date Time Calculator 1.0-beta-4.21

Updated the default filter hook values for gpdtc_add_delta_warning_entry_note and gpdtc_email_admin_on_rejected_calc to false.

Fixed an issue where Time fields with 24-hour format would not calculate correctly in some situations where the hour is set to 00.
Added "Update URI" to plugin header to improve security.

Fixed issue where Date Time Calculator failed to generate timestamps for Read-Only-enabled Date & Time fields.