Account creation interface and network operations.

Hooked up keyboard “next” and “done” keys on login page
and for captcha text box keyboard on both account creation
and section editing interfaces.

Nav bar "check" button on login and account creation interfaces
now changes color once minimal required data has been entered.

Editing captcha image retrieval now occurs on background thread.

Fix for iOS 7 bug which caused 3 little blue dots to appear
in navigation bar briefly during animations.

Handles nav bar button taps more consistently.

Fixes for nav bar night mode for iOS 6.

Pulled captcha interface out into own view controller.

Fixed bad bug with “insertPlaceHolderImageEntityIntoContext” which
was unnecessarily adding duplicate image records.

Separate ops for search results and search result thumbnail url
retrieval.

"No results for search term" message shown when approriate.

Better search result error handling.

getImageOfColor now works with iOS 6, uses only a single filter
instead of two, and also works with monochrome color space colors.

iOS 6 main menu fix for offline reading animation having white background.

iOS 6 main menu fix for thin gray horizontal line appearing if menu is
loaded before any articles have been loaded.

Change-Id: Ia52d79bab92ef98fdcab023849e1286d6ca312a8