Advanced search data sources reworking

[DominicBM]

It's been suggested that we rework the data sources on the advanced search to simplify and clarify. Ideas:

• Combine "archives.gov" and "presidential libraries" into one "web pages" option.
• "Archival Descriptions", "Archival Descriptions with digital objects" and "Presidential/Vice Presidential Electronic Records" should also all be one source.
• Within this, you should be able to select/unselect "Available online only" and expand/collapse fields specific to the presidential electronic records.

[DominicBM]

No specific requirement, but I think R1P2I1 design mockups address this.