Add to subset of DCMI Type in resource_type CV, perform large-scale metadata remediation

[briesenberg07]

Desired fixes

1. Update OD2/config/authorities/resource_types.yml to include http://purl.org/dc/dcmitype/StillImage
2. For OD works with still-image file formats such as .jpg, .tiff, .png, etc. [1], change resource_type value from http://purl.org/dc/dcmitype/Image -> http://purl.org/dc/dcmitype/StillImage

Justification

OD2/config/authorities/resource_types.yml currently implements a subset of the DCMI Type vocabulary including dcmit:Image and dcmit:MovingImage, but not dcmit:StillImage.

dcmit:Image has been used in OD primarily to indicate dcmit:StillImage resources [1]. This current usage is not strictly speaking incorrect, but is insufficiently specific, as Image is defined to include both still and moving images. [2].

---

[1] See faceted Solr query results: file format values for OD works where resource_type = dcmit:Image -- overwhelmingly still-image formats with a very small number of moving-image formats

[2] dcmit:Image is a superclass with subclasses dcmit:MovingImage and dcmit:StillImage.
Turtle snippet from DCMI Metadata expressed in RDF Schema Language > DCMI Type Vocabulary

<http://purl.org/dc/dcmitype/Image>
    dcterms:description "Examples include images and photographs of physical objects, paintings, prints, drawings, other images and graphics, animations and moving pictures, film, diagrams, maps, musical notation.  Note that Image may include both electronic and physical representations."@en ;
    a rdfs:Class ;
    rdfs:comment "A visual representation other than text."@en ;
    rdfs:label "Image"@en .
<http://purl.org/dc/dcmitype/StillImage>
    dcterms:description "Examples include paintings, drawings, graphic designs, plans and maps. Recommended best practice is to assign the type Text to images of textual materials. Instances of the type Still Image must also be describable as instances of the broader type Image."@en ;
    a rdfs:Class ;
    rdfs:comment "A static visual representation."@en ;
    rdfs:label "Still Image"@en ;
    rdfs:subClassOf <http://purl.org/dc/dcmitype/Image> .
<http://purl.org/dc/dcmitype/MovingImage>
    dcterms:description "Examples include animations, movies, television programs, videos, zoetropes, or visual output from a simulation.  Instances of the type Moving Image must also be describable as instances of the broader type Image."@en ;
    a rdfs:Class ;
    rdfs:comment "A series of visual representations imparting an impression of motion when shown in succession."@en ;
    rdfs:label "Moving Image"@en ;
    rdfs:subClassOf <http://purl.org/dc/dcmitype/Image> .