Change interfaces to abstract classes
+ create AbstractMetricPlotFetcher
+ refactor MonitoringMetricPlotFetcher to fetch data with batches
+ refactor CustomMetricPlotFetcher to avoid copy-past in code
+ add displayName to Monitoring MetricNameDto when creating control tree
+ add check for null after splitting monitoring metric name.
Merge pull request #460 from kgribov/InterfaceToAbstract

615 Switch listeners from interfaces to [abstract] classes.
+ replace catch for NPE with if clause
Merge pull request #463 from amikryukov/fetch-monitoring-plots

JFG-672 Improve fetching of monitoring plot data
merge with master