Top nav bar controls now easier to customize.

When edit icon tapped, keyboard now appears when wikitext loaded.

Editing page controls now much closer to mockups.

Fix keyboard issue when selecting text from editing text area.

Fix keyboard hiding issue with main menu.

Made category on UIViewController for easily hiding keyboard
regardless of which view is first responder.

Made custom search nav bar use constraints for positioning
itself and subviews.

Change-Id: I25b5535439f5ca87b7331fb4ac37470c91e66163