Reference-Sequence Conversion Improvements for Merging

* Pass BED "track", "browser", etc. lines unmodified.
* A reference can now indicate it is a combination of multiple other references.
* Remove redundant print in `genome feature-list merge` since it will be printed by the import command.
There is.

```
genome=> \d feature_list_name_key 
      Index "model.feature_list_name_key"
 Column |          Type           | Definition 
--------+-------------------------+------------
 name   | character varying(1500) | name
unique, btree, for table "model.feature_list"
```