refactor EntryValidator to IEntryValidator
minor cleanup
move IRegionSelection and RegionSelection to selection package
add region selection providers

add IRegionSelectProvider

include methods for getting/setting IRegionSelectProvider in IProviderManager

update InternalProviderManager and ProviderLoader

add GenericsSelectionProvider and WorldEditSelectionProvider internal classes

If a provider is not installed, the WorldEditSelectionProvider is used as default unless WorldEdit is not installed, in which case GenericsSelectionProvider is used.