Improved code of methods in Messages.Utils. Locale search given a
display name is handled by the getLocale(String) method.
Updated GUI to merge my work with Liz's work. I also improved the Action
handler on language switch to avoid having 2 if and 2 for nested
statements (only 2 if statements with a more explicit code remain).

I'll be deleting the MainWindow class once the GUI class is fully
updated.