Schema refactor and other fixes.

Added mime type to core data image entity.

Added dateLastAccessed to core data image entity.

Simplified article core data schema.

Converted site and domain entities to attributes of article entity.

Converted discovery method entity to attribute of history entity.

Added new "onlyrequestedsections" api parameter.

Also saving section anchor to section core data entity.

Moved getArticleForTitle out of web view controller.

Change-Id: I689e802101741239288e922a26c7b1f3c5468f3d
Core data concurrency refactor.

Change-Id: I110790c9d61755c46bcbdd4d57adeab5cf3fda0a