Redesign how shift times history is saved. Previously it stored the
localized strings in the history file, which are not particularly
parsable as the format may differ between locales. Rather than doing
this, store the raw settings in a json file, and generate the history
strings on display. In addition to making it much easier to load old
settings, this makes it so that the history is always displayed using
the current locale, rather than the locale in which the shifting was
done.
Closes#1427.
Originally committed to SVN as r6363.