Extract the components and rework as avisota/contao-core package.
Extract components into partial projects.

Extracted projects:
- avisota/contao-message
- avisota/contao-message-element-article
- avisota/contao-message-element-event
- avisota/contao-message-element-gallery
- avisota/contao-message-element-headline
- avisota/contao-message-element-hyperlink
- avisota/contao-message-element-image
- avisota/contao-message-element-list
- avisota/contao-message-element-news
- avisota/contao-message-element-table
- avisota/contao-message-element-text
- avisota/contao-renderer-backend
- avisota/contao-renderer-mailchimp
- avisota/contao-salutation
- avisota/contao-subscription-member
- avisota/contao-subscription-recipient
Remove conflict from composer.json.
Fix a lot of class reference and namespace issues.
Fix dc-general dependency.
Fix @package definition.
Add .skip to .gitignore.
Add dependency contao-community-alliance/backports-initialize-system.
Move the old database.sql backup.
Disable the database.sql.
Remove dynamics.php.
Fix class and namespace issues.
Extract some services into other modules.
Extract the salutation module related files.
Extract recipient related settings.
Rework the service generation.
Remove non existing field from palette.
Fix the data provider class.
Remove deprecated dca_config class definitions.
Update dependencies.