Operations for login, login token, and edit token.

Added login option to main menu.

Refactored code which presents view controllers out of WebViewController.

Disabled auto-correct for captcha text box.

Fixed annoying hiding of keyboard when all text removed from search
input box.

Added error messages for login error types.

Now tries to get edit token for the language of the article being
edited so authenticated user can switch language and still have
edits associated with their account.

Change-Id: Iaacd6908fa3e1e963c6a010c69e2e1afb9cbb769