highlight "child" sources more intentionally their source homepage

[rahulbot]

We do allow multiple sources with the same name, iff they have a url_search_string set. Those are "child" or "placeholder" sources. I suggest we add some things to highlight when a source is a "child" source. Some ideas:

• add "child source" after header name
• add item to details list that says "parent source:" and includes name and link to the parent (same name, no url_search_string)

[rahulbot]

Bonus feature would be a table on the "parent" source page listing all the child sources (ie. source that have same domain name and also url_search_string set)