Move all setting/getting of login details to LoginUtils.
LoginUtils: Encrypt/Decrypt the auth name and auth key.

This does not provide much real extra security. The SharedPreferences
are already private as long as you do not have root access.
But this obfuscates against very casual browsing and avoids us
having to explain why encryption isn't really useful or
necessary.
DecisionTreeTest: Fix the build.
ItemsContentProvider: Add a comment about how the server doesn't fail on bad credentials.

It would be nice if it did.
LoginActvity: Try to stop autocorrections in the username.

Apparently this is the most reliable way to do this, though even
then it depends on the (bugs of the) input method being used.
QuestionHelpFragment: Really add space between the example thumbnails.