JFG-783 Change line - legend relation in all plots

+ creating PlotSeriesDto object , that represent single plot, from one place for metric and plots.
+ MetricDto do not contain superfluous PlotDatasetDto that represent same values from MetricDto.values in other way.
+ create legend tree.
- plots rendering in old way
- new legend tree presents in  panel bellow plot
LegendProvider requires re-factoring:
1. private String generatePlotHeader(String sessionId, String taskName, String plotName)  is not used
2. public String getPlotHeader(Set<Long> taskIds, String plotName) is very strange, in the place, where it is called all necessary data is available, but instead of using this data we are going to DB