Motivation:
ChannelsSelectionModel.qml is freezing the app when used with a live channel that's being edited because on each channel change the selection model is re-created.
The fix for this is to use the LeftJoinModel to unify the channels selection (a light model containing only keys) and the full channels model containing the channels data. On top of this, the SortFilterProxyModel is added to decorate the model with the roles expected in the UI. Another improvement is by replacing the ExpressionRole with the FastExpressionRole.