Calendar sync improvements

We’ve made lots of improvements under the hood of calendar list syncing.

Adding or removing a calendar external (e.g., in Google Calendar) now is reflected instantly in Cron. The change also fixes a teammate’s calendar not appearing in “Meet with” if the calendar has been manually shared and toggled its visibility off. Finally, it also fixes not able to hide calendars reliably in specific scenarios.

Other improvements

• Adds hover state for in-app notification messages (bottom-right “toasts”).
• Simplifies body texts of toasts.
• Disables entering “Share availabilities” from “Meet with” and vice versa.
• Disables selecting events from the menu bar calendar when a modal dialog is visible.
• Fixes not able to change an event’s calendar in specific scenarios.
• Fixes bad request when changing time zone after toggling all-day.