Major changes in 3.15.3:
* Initial search implementation
* Month-view reworked
* Month-view support for overflow of events
* Month-view has support for RTL locales
* Month-view has support for multiday events
* Edit/new dialog reworked to use GtkBuilder UI files
* Added new time and date selectors
* Added proper `GtkHeaderBar`
* Added calendar selector popover for when the dialog is used on event
* Added calendar selector popover for hide/show calendars on the main window
* Navigation buttons were relocated and a Today buttong was added
* Calendar got a new 3d icon