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.