feat: Adding the option to display year in time applet

[DracoTomes]

As worked out in #1238 the switch from fieldsets::long() to fieldsets::medium() causes unsightly behavior on some locales. The feature to display the year was requested there and can cover up the ., combination.

[DracoTomes]

Additional note: Yesterday when having a look at this I also tried out a match style pattern to make it easier to add more flags in the future. As a rust noob this required some ugly encapsulation and honestly I found the result harder to read and understand than the if/else structure currently in place.

let fs: CompositeDateTimeFieldSet = match(self.config.show_date_in_top_panel, self.config.show_weekday, self.config.show_seconds) {
    (true, true, true) => CompositeDateTimeFieldSet::DateTime(DateAndTimeFieldSet::MDET(fieldsets::MDET::medium())),
    (true, true, false) => CompositeDateTimeFieldSet::DateTime(DateAndTimeFieldSet::MDET(fieldsets::MDET::medium().with_time_precision(TimePrecision::Minute))),
    (true, false, true) => CompositeDateTimeFieldSet::DateTime(DateAndTimeFieldSet::MDT(fieldsets::MDT::medium())),
    (true, false, false) => CompositeDateTimeFieldSet::DateTime(DateAndTimeFieldSet::MDT(fieldsets::MDT::medium().with_time_precision(TimePrecision::Minute))),
    (false, false, true) => CompositeDateTimeFieldSet::Time(TimeFieldSet::T(fieldsets::T::medium())),
    _ => CompositeDateTimeFieldSet::Time(TimeFieldSet::T(fieldsets::T::medium().with_time_precision(TimePrecision::Minute))),
};
DateTimeFormatter::try_new(prefs, fs)
    .unwrap()
    .format(&datetime)
    .to_string()

Also so far I've compiled and ran that version of cosmic-applet-time from the shell which respected the config flags but I haven't found a way to test the vertical orientation yet.