Fixes: 1) Correct avatar resolution in `resolve_avatar` method for cases where `url` or `name` attributes are missing; 2) Refresh user object from the database after avatar update to avoid stale data;
Extra: 1) Rename `BulkActionOrderProductInput` to `BulkProductInput` for consistency; 2) Minor code refactorings and adjustments for clarity.
1) Userless orders will be merged on user's registration by their phone number and/or email. Added Viewset action "merge_recently_viewed" so recently viewed products may be stored on server's side.
2) Added comprehensive products' filtering by category(support for including subcategories)
Fixes: I18N
