Improved repository status tracking

[AMDmi3]

Currently repository status updates (new → active ↔ legacy) is not really tied to actual repository updates and thus not always correct. Improvement is needed, which may use the following logic: instead of deprecate_repositories+add_repositories in database_update_pre, compare list of repositories in the database with list of repositories from config. Added repositories are inserted with new status (and here we have chance to carefully choose unused ID and avoid problem with autoincremented smallint ID overflow), removed repositories are switched to legacy status. Then after updating packages, actual repositories are marked as active. This is also compatible with future per-repository updates.

While here, can also

• add json metadata field for Generalize repository metadata handling #735 (without removing existing columns yet for comatibility)
• add last_updated field for Introduce repository update periods #972
• move ruleset hash into repositories table, as it currently resides in the separate table for no apparent reason