components/calendar & applets/digital-clock: Something about premium edition

It's time to

This patch set probably contains a bit more than adding some standard spacing to the layouts.

Most notable fixes (in no particular order) include:

• Week numbers aren't glitched anymore for previous/next months;
• Reduce visual glitches when resizing the view (by disabling SwipeView's animation, by temporarily resetting currentIndex to -1);
• Fix prematurely saving selected time zone to configuration before applying (saving) the newly added time zones — this has caused some nasty "undefined" errors;
• Errors are fixed in the code too, so it is overall more robust against unknown time zones now;
• Reset currentIndex of a header TabBar when leaving it through keyboard navigation;
• Highlight an explicitly added time zone which resolves to the same time zone as "Local" just the same as it would've highlighted the "Local" time zone itself — both in Time Zones view and in the applet's tool tip.