Fix 'Hardly distinguishable line colors in reports'

The color palette used for a diagram can now be modified in
individual reports.

Note: In KReportConfigurationFilterDlg::slotSearch there is redundant code
for casting eMyMoney::Report::ChartPalette to int which is already implemented
in xmlstoragehelper.cpp.

BUG:408361
FIXED-IN:4.8.4,5.0.6
Differential Revision: https://phabricator.kde.org/D22293