Better group properties handling

Description

Currently the DefaultGroupPropertyMap's interface is java.util.Map. Group properties are passed around as plain maps, which obscures the fact that they are actually being persisted.
Adding a PersistableMap interface/abstract class and using this to pass DefaultGroupPropertyMaps around will make the intention more visible. This is not a functional change, it is purely cosmetic.

Environment

None
Fixed
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Assignee

Alex Mateescu

Reporter

Alex Mateescu