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.

Launcher buttons now respond to HiDPI scale factor changes to ensure
icons are reloaded at the new scale when settings change without having
to restart.

Panels now respond to HiDPI scale factor changes without requiring
a restart. When the monitors-changed signal is received, the panel
updates its scale factor and forces applets to redraw at the new scale.

The temporary size change (to 0 and back) is necessary because applets
don't individually listen to scale change signals.

This eliminates the need for mate-settings-daemon to kill and restart
mate-panel when the scale factor changes.

mate-panel uses libsoup indirectly through libmateweather, which already
requires libsoup-3.0. Evolution Data Server (used by the clock applet
for calendar integration) also requires libsoup-3.0.

* 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.

A previous overzealous cleanup left some hanging screen variables and
one instance of an uninitialized screen being used.