Add context predictate to view configurations

Up to now things like /stream/embed.js just worked too.
Merge pull request #1363 from Treora/fix_view_contexts

Add context predictate to view configurations
Refactor API code to use annotator-store flaskless
Process pull request feedback
Remove unused imports
Remove _url_for
Fix anonymization of deletes
Code style and formatting cleanups

- Collapsed some long long lines
- Consintently use single quotes everywhere
- Fix some indentation
- Fix some whitespace issues
Rename FIELDS_SET_INTERNALLY to PROTECTED_FIELDS
Add logging messages in __init__.py
Open Annotation support using JSON-LD
Define has_target