OPENDJ-2539 - Control-Panel: Nothing displayed in Monitoring > General Information > Db Env
Now that we have pluggable backends, the name of entries containing the monitoring information for databases has changed, and there are 2 kinds of statistics : for JE and for PDB.
BackendDescriptor.java: Adds support for the type of pluggable backend (JE or PDB)
DBEnvironmentMonitoringPanel renamed as DatabaseMonitoringPanel, added support for type of pluggable backend. Renamed "operations" into "fields" (these are the statistics attributes we display).
DBEnvironmentMonitoringTablePanel renamed as DatabaseMonitoringTableModel, code cleanup.
BrowseGeneralMonitoringPanel.java: Replace DB Environment node by 2 Databases Information Nodes : one for JE backends, one for PDB backends
GeneralMonitoringRightPanel.java: replaced the DBEnvironmentMonitoringPanel by 2 DatabaseMonitoringPanels (JE and PDB), reworked identifications of all panels (to avoid using className).
ConfigFromDirContext.java: added detection of backend type in monitoring entries.
MonitoringAttributesViewPanel.java : code cleanup
admin_tool.properties: Update messages.

The stats panel have a button called "Show Operations...". The term Operations is ambiguous and not exact in the DB stats, but code and labels are shared with ConnectionHandler stats, so I've left them like this for now. In the future, this should be cleaned and reworked.