Overhaul the directory datastructure to include "Domain" as a child of "Source", to cover cases where a source has changed its domain

[pgulley]

This is a pretty major database structure change- add a new layer of abstraction, differentiating between a "Source" - representing a news outlet in the most general sense- and a "Domain" - representing a specific webpage which we attempt to index content from. A source should be able to have multiple Domains.

[rahulbot]

Any simplicity to be derived by making that a source_aliases table instead of a source_domains table? That would allow source.name to still exist as the primary domain like it is now, but allow a small number of sources to have optional entries in the "alias" table. We'd add a button to the source editing page that allows for converting, creating an entry in alias tabe, automatically copying over feeds, and then deleting. Just wondering if that simplifies for this edge case, or is more complex.