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If KOrganizer shows the agenda view when it launches, and then is
switched to the timeline view, the timeline gives too much space to
the calendar list and too little to the time grid.  Also, when the
main window is resized, the calendar list is not resized.

This patch sets the initial panel sizes and resize behavour, which
makes `splitterMoved()` redundant.

When `TimelineView::showDates()` attempts to get the user's preferred
calendar colors, `preferences()` returns an empty object, and the view
ends up using random colors for the time blocks.

When a recurring event is moved, a dialog box asks which instances to
move.  Apparently `mActionItem` can be set to null by asynchronous
events while the dialog is up.

BUG: 435352

A disassociated occurrence of a recurring incidence can be left behind
when the recurring incidence is deleted, due to bugs.  This patch makes
them visible, for robustness, so they can be cleaned up.

GIT_SILENT: add sanitizers.supp so we can suppress some leak generated by some lib (as libfontconfig)

The user interface uses "tag" and "category" as terms for the same thing.
Settle on "tag", for consistency among Akonadi applications.

GUI: