Improvement: webclient: Cache summary/plot data

[amikryukov]

Not an Issue, but an improvement

Problem

Currently, web client re-read all data from database if you click on metric/plot several times.
The same happens, when you choose many sessions and many plots, and afterward, decide to remove one session from the view. It leads to all data to be fetched from DB one more time.

Implementation Details

Sessions changed:
SessionSelectChangeHandler calls #updateControlTree every time session is changed which leads to all Metric/Plot panels to be cleared, and all checked metrics/plots to be downloaded.
Almost the same happens when you check/uncheck plot for particular metric in DetailsNodeHandler

Technical Details

Inside Trends.java web client already store the plots, and summary metrics, which are downloaded and should be shown.

public class Trends ... {
  ...
  private HashMap<MetricNode, SummaryIntegratedDto> chosenMetrics = new HashMap<MetricNode, SummaryIntegratedDto>();
  private Map<MetricNode, PlotIntegratedDto> chosenPlots = new HashMap<MetricNode, PlotIntegratedDto>();
  ...

But by design, plot/metric name (MetricNameDto) has a link to session ids which are chosen (via TaskDataDto).

That is why it should be designed before an implementation.