New: Initialize plugins with the current instance

Plugins are now instantiated with a reference to the parent diva instance in the init function
New: Initial commit of the highlight plugin

Provides a generic method for highlighting a region of a given page.
Fixed: Rename events to a more generic name

Since events may be used to do more than just update the toolbar, their name should reflect this.
New: First pass at an annotate plugin

Just a placeholder for now, doesn't do anything.

Refs #116
Fixed: Formatting
New: divaserveURL config parameter is now objectData

This makes it clearer that Diva can be operated by simply serving a cached JSON file, rather than needing the divaserve script to serve the JSON.
New: A text view plugin

Nothing here yet.
WIP: Updated highlight plugin
Fixed: Other code for the objectData switch wasn't committed.