Bug: Caption in historical charts with sparse weight entries

Calculation of trend analysis for the caption of historical charts was incorrect for periods with sparse weight entries. Instead of replicating the trend for days without weight entries as {\tt history::analyseTrend} does, the chart generator only released trend values to {\tt addPoint} for days which had weight entries. Since the trend fitter assumes continuous data points, this resulted in a gross overestimate of the slope of the data, resulting in inflated weight and energy balance values in the chart caption. I modified the {\tt history::getDays} function to fill in trend values for days with no weight entry as {\tt analyseTrend} does. Values in chart captions now agree with those calculated by the trend analysis page for equivalent intervals. (Reported by Lorenzo Emilitri.)