Views integration needs love

Workin on it.

This patch addresses all of my earlier feedback:

>There's no way to filter for parent/child notes

The parent field now allows filtering by empty or not empty, so if you wanted just parents you would filter by notes with an empty "Parent note" field.

>Some Moderation Note fields have the same label - there are a ton that have the copy+pasted label "Entity"

Fixed across the board.

>When rendered in a view, notes should have that "View notes in context" button

I changed the logic so that the view in context button shows up when notes are being rendered in the "Preview" view mode. I also added a new Views field plugin that renders the same link to view the note in context.

>Entity reference fields on Moderation Notes should have exposed filters that use autocomplete

I added this for the Author and Assignee field, and both appear to work.

I moved the method to get a link into a proper URI callback, so you can call $note->toUrl() now.