Saves section edits.

-Core data Image(s) for Section creation moved into
category on Section.

-Alerts and network activity indicator decoupled from
web view controller.

-Basic alerts added to section editing.

-Refactored so single “displayArticle:” method sends html
across bridge.

-Thumbnail from core data store retrieval now grabs highest
resolution version of the image it can find.

-1st pass at dedicated operations for retrieving article
sections.

-Section wiki text loading and saving operations.

-User alerted to server wiki text saving errors with
error message from server.

Change-Id: I115e60fc74f1d73e317ce18959af63cfbbbe6578