feat: extend SQLite schema

[botprzemek]

Add #12 suggested tables:

• users, org
• companies_lists, org companies -> lists (many-many)
• lists_tags, org lists -> tags (many-many)
• campaigns, org
• campaign_steps, org campaign -> step (n-many)
• mail_templates, org
• mail_queue, org

As values (TEXT e.g. display_name "foo") or feature flags (INTEGER e.g. dark_mode 1/0 [on/off])

• organization_settings, org, organization -> settings (n-n)
• user_settings, org, user