* Emit a signal when the Pipeline gets started.
* FlexibleView now can be initialized with an additional header widget.
* QueueView waits for the Pipeline to become ready.
* PlayableModel::ensureResolved() passes queries in one batch to the Pipeline now.
* DbCmd_PlaybackHistory can now deal with date ranges.
* RecentlyPlayedModel can now deal with date ranges.
* HistoryWidget is a FlexibleView with date range input fields as an extra header.
* Forgot to add HistoryWidget to CMakeLists.txt.
* SourceItem now uses HistoryWidget to display recently played tracks of Sources.
* Slightly different tooltips for the gauges.