The Appointments and Tasks expanders in the calendar popup were
incorrectly linked to the show-calendar-events and show-tasks gsettings.
This caused collapsing the section to toggle the preference, making the
entire section disappear on next popup.

Fixed by adding a new expand-calendar-events and expand-tasks gsettings
keys to track the UI state separately from whether the section is
visible or not.

Evolution tracks a color for each calendar. We can fetch this to
differentiate events from multiple calendars in the popup.

This also marks the current event in bold and scrolls the window to make
it visible to the user on load.

* clock: Store calendar client in ClockData

This simplifies the evolution calendar client architecture and makes the
popup show up faster, since we don't need to create a new one every time
we open it.

* clock: Fix calendar data refresh when opening popup

The calendar popup was not showing recently added Evolution
events/tasks. Added a refresh timeout call every time the calendar popup
opens. That way the popup opens immediately and the data is refresh
after a small delay.

Add Evolution Data Server (EDS) calendar integration to the MATE panel
clock applet, most of it ported from gnome-panel's clock applet. This
allows users to view calendar events and tasks directly from the clock
popup calendar.

The calendar integration is disabled by default and can be enabled
with --enable-eds during configuration. When disabled, the clock
applet functions normally without any EDS dependencies.

Mostly found by cppcheck.

origin commit was:
https://github.com/mate-desktop/mate-panel/commit/96c7ebc

This reverts commit 96c7ebc6dc9e8b8327db04a9570054ee78743353.

Mostly found by cppcheck.