Fixes to generic index file.

It got messed up accidentally by 7cf0fc1451456e7dd19283ca524bf7e46151a999.
Factored out abstract storyline layout code; some cleanup and improvements.
Factored out the entity line normalization and link building code.
Fix to storyline node classes and select handling.
Removed testing stuff.
Don't add empty years to the entities table.
Storyline manual query mode includes cooccurrences like facet mode.
Storyline defaults to query mode if default facet is null.
Config file option to set the data field the storyline uses to define clusters.
Factored out list of data fields from help text.
Clear query button for storyline query mode; update button has primary button style.

The clear button is so the help message can come back without refreshing the page.