[Database] Switch to cascading deletes in the DB layer where possible + some cleanup

[EricWittmann]

This PR includes the following DB changes:

• Add ON DELETE CASCADE where appropriate to FKs
• Add FK from artifact_branches to artifacts table
• Rename globalrules to global_rules
• Rename rules table to artifact_rules
• Rename artifactreferences table to content_references
• Rename artifactreferences column on content table to refs
• Rename comments table to version_comments
• Organize/group table definitions within DDL file
• Create new group_rules table (future need)
• Standardize on seq_name and seq_value for column names in sequences table
• Reduce max label value column size to 512
• Add INDEX on label value columns for mssql DB flavor

[github-actions]

Qodana Community for JVM

31 new problems were found

Inspection name	Severity	Problems
Unnecessary modifier	🔶 Warning	18
Overly complex class	🔶 Warning	3
Class with too many methods	🔶 Warning	3
Overly long lambda expression	🔶 Warning	3
Magic number	🔶 Warning	2
Overly coupled class	🔶 Warning	1
Unnecessary Javadoc link	🔶 Warning	1

💡 Qodana analysis was run in the pull request mode: only the changed files were checked
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