Issue 256 Work on re-organising the Database Section of Framework

docs/core/architecture.md

docs/extensions/civix.md

docs/framework/database/index.md

docs/framework/database/schema-definition.md

docs/framework/database/schema-design.md

docs/img/mysql_workbench_civicrm_country_foreign_keys.png

docs/img/mysql_workbench_civicrm_country_tables.png

mkdocs.yml

redirects/internal.txt