For each report format add a `<Report format> warnings trend graph (totals)` portlet. It would be nice to have one generic portlet entry which allows to configure
the display name of the portlet
width / height of the graph
the number of days to consider
the type of report format (CheckStyle, CPD, SpotBugs, ...)
By having only one generic portlet entry we would avoid to overload the dropdown component with too many entries.