Categorize lead_art_provider

[livlab]

Create a category system to classify lead_art_provider by source, as follows:

• NPR (NPR, * for NPR)
• External Source (AP, GettyImages, Courtesy of * and all other sources)

This will allow easier comparison by source.

[livlab]

OR,

• [x] classify by source name as is, only consolidate into categories the following:
• * for NPR
• Courtesy of *

[livlab]

After discussion, decided to categorize into:

• NPR (includes NPR and * for NPR)
• Wire (AP)
• Stock (includes Getty, iPhoto, Corbis)
• Other (all other sources including "courtesy of")