Added custom ReadOnlyCollection
Started integrating new domain model into FIVES

Extracted PluginManager into a separate project in Core
Renamed all core namespaces to FIVES
Adapted all plugins to use new domain model except Persistance
Converted several internal Lists into Dictionaries for efficient access
Made all event args public (to allow users simulate events)
Renamed Entity(Added|Removed) into (Added|Removed)Entity
Moved NativeClient project into Misc folder
Added test plugin projects into Misc
Removed fixed test plugins - they will now be generated on build
Updated plugin manager test to use new test plugins
Corrected failing tests