PHP8, env vars instead of settings.php, misc other changes

[craigk5n]

• Updated some dependencies. PHPMailer updated to 6.8.0, which includes PHP8 support.
• Reordering of includes broke view_entry.php
• Refactored includes/config.php. The do_config function in config.php has been updated to allow using environment variables to set WebCalendar settings normally found in the includes/settings.php file. This will allow users to more easily use docker to run WebCalendar. The install pages still need to be updated to handle upgrading a database that uses env vars.
• Fixed many PHP8 warnings/errors
• Added new bump_version.sh script that can be used to update the WebCalendar version number is all the right places.