[applets/digitalclock] Fix showing agenda view when enabling first event source
The agenda view is only shown when at least one event source is active. When going from 0 to 1 active sources the view wasn't updated correctly.
This was because the visibility of rightColumn was bound to the visibility of its child, but since the visibility of the parent affects the visibility of its childred (https://doc.qt.io/qt-5/qml-qtquick-item.html#visible-prop) that resulted in a broken binding.
Bind to the source property directly to avoid this
Edited by Nicolas Fella