major: refactoring, renamed group(s) to show(s) in backend

api/v1/api.go

api/v1/api_files.go

api/v1/api_imports.go

api/v1/api_playlists.go

api/v1/api_shows.go

api/v1/api_uploads.go

api/v1/types.go

cmd/tank/main.go

contrib/mariadb-stretch-err1071.md

contrib/mysql/info.sql

contrib/mysql/test-fk.sql

contrib/postgres/info.sql

contrib/postgres/test-fk.sql

contrib/run.sh

importer/fetch.go

importer/importer.go

importer/job.go

importer/job_inventory.go

importer/normalize_converter.go

store/files.go