Redesign the Plasma Calendar applet
This MR contains 5 commits, I tried to separate them the best I could, but they still all depend on each other:
- This removes the grid around the items
- The header component was moved to the MonthView instead of being contained in the DaysCalendar. It is also now optional and the API caller can disable it. It also now use buttons to navigate to year/month/decade view instead of a non-discoverable click on the heading
- It is now using a SwipeView to provide better touch navigation. I also added some convenient functions to manipulate the view and get its state and a bit of documentation
- Use a correct highlighting for the calendar view using PlasmaComponent2.Highlight
- Make the content size of the calendar views consistent. (taken from Jan's MR)
The 4 first patchs are released under LGPL-2.0-or-later while being in a GPL module.