Annotation motivations

[csarven]

Add additional annotation motivations and purposes. Currently we use oa:replying, oa:commenting, oa:describing, oa:assessing, oa:bookmarking for motivations, and oa:describing and oa:tagging for annotation purpose.

Consider adding specific styles for each motivation eg., edited annotation can use a different background colour?

[csarven]

Using Web Annotation's vocabulary with built-in motivations, below is a table covering three types of actors and checkmarks on those applicable to them. There is overlap, so it is not a strict division between the motivations. The UI should reveal relevant motivations depending on whether the user is in authoring, social, or editorial/review mode. There can be other actors (or modes), but we can start with this for now. Some of the motivations may not need to be an annotation action and preserved in data eg., authors actions linking, identifying, classifying, or tagging are generally part of the authoring process by default. I think it makes more sense to use them only in context of the non-authoring modes. On the other hand, the describing action can be used by the author for additional information eg. footnotes (this is currently implemented)

motivation	authoring	social	editorial/review
bookmarking		✓
classifying	✓	✓
commenting		✓
describing	✓	✓
editing			✓
highlighting		✓
identifying	✓	✓
linking	✓	✓
moderating			✓
questioning		✓
replying		✓
assessing		✓	✓
tagging	✓	✓

There can be more motivations. There is some overlap with social activities (eg ActivityStreams' inReplyTo).