Eliminate use of Android-private APIs for getting user-selected

date/time formats.  With this change, K-9 can run on original master
or cupcake versions for the platform.

This seems like an excessive amount of code.  Perhaps there is a
public API that accomplishes this work.  Alternatively, the code in
MessageView.java and FolderMessageList.java should be consolidated
into a utility class used by both of the classes needing this
functionality.