First pass of a v4 cookbook

[glenrobson]

Steps for adding a v4 recipe for example 0001-mvm-image:

1. Make a directory in 0001-mvm-image called v4.
2. Rename the index.md in 0001-mvm-image to recipe.md
3. copy everything in 0001-mvm-image to v4
4. Edit the manifest.json and recipe.md in v4 to make it work for v4
5. Add a index.json similar to the one in this pull requests which will show both recipes.

Notes:

• Frontmatter is only present in the index.md parent recipe so all topics, viewers and other things need to go in this file rather than the child recipes
• added a new field to index.md v4-viewers to list v4 supporting recipes
• Need a more elegant way of linking to v3 only recipes in a v4 recipe.
• Maybe highlight which versions of a recipe are aviliable when linking to a recipe.
• Will need to think about validation of v4 and sending v3 files to v3 validator and vise versa.

[glenrobson]

Example v3 and v4 recipe: https://preview.iiif.io/cookbook/v4/recipe/0001-mvm-image/

[glenrobson]

Point to version 4 of the spec: [language map][prezi3-languages]

[stephenwf]

@glenrobson I've temporarily fixed the Audio/Video Presentation 4 support in Theseus. (Until the parser has full support for the 3D additions)