Singleton: Specify a language (en) when using toLowerCase().
ListFragment: Remove an unnecessary try/catch.
LoginUtils: Explain why we catch an unchecked exception.
Don't catch (unchecked) ActivityNotFoundException exceptions.

Because those would be serious programming errors that we could not
recover from. It would be better to let the user report the crash
with a stacktrace, rather than just ignoring it, in the theoretical
case that this happened.
Minor comments/logging improvements to catch blocks.
Don't catch some unchecked exceptions.

These would be programmer errors that the user should be able to report
to us with a stacktrace. We could not recover at runtime.
QuestionFragment: Throw a RuntimeException if we couldn't store the classification.

It should never happen but ignoring it would mean a silent loss of data.