WP Mail SMTP Pro 4.2.0

### Added:
- Email Log: save and display the email sending errors in email log entries.
- Email Log: button to delete all email log entries at once.
- Email Log: display a proper delivery status for each sent email for these mailers: SMTP.com, Sendinblue, Mailgun.
- Other SMTP mailer password encryption/decryption.

### Added:
- Email controls to disable plugin and theme auto-update emails.
- New Amazon AWS SES regions: London, Frankfurt, Ohio, Canada (Central), Mumbai, Tokyo, Seoul, Singapore, Sydney and São Paulo.
- Amazon SES Mailer: support domains verification.

### Changed:
- Sendinblue SDK library version to 6.4.
- Google apiclient library version to 2.7.
- Improve plugin settings input and toggle focus states.
- Amazon AWS SES library. Migrated to the official AWS SDK library.

### Fixed:
- Email controls to disable user and site registration/creation/activation.
- Hide admin bar menu when errors are present and the "Hide Email Delivery Errors" setting is enabled.
- CSS sourcemaps warning messages in browser dev tools.
- Zoho mailer issue with comma in the "from name" field.
- Action Scheduler tasks being registered too early and not getting assigned to the plugin group.
- PHP notices in Amazon SES mailer automatic region detection.
- Admin bar CSS asset loading when the admin bar is not showing.
- License key verification triggered on non license plugin settings input enter event.
- Fatal error on plugin uninstall if `ActionScheduler_QueueRunner::unhook_dispatch_async_request` method does not exist.
- PHP Deprecated notice for `base_convert()` function usage in the Mailgun mailer.