SLanguageId created
SLanguageIdImpl created
created SConceptId interface
SConceptIdImpl created
create DebugRegistry
DebugRegistryImpl created
remove mentioning of tree repository structure as it makes things more complicated and doesn't really work
SConceptIdImpl: equals and hashCode
SChild/Ref/PropId created
SLanguageId: equals and hashCode
ConceptRegistry: remove deprecated stuff
SChild/Ref/PropId created
SxxxIdImpl (Link, Child, Property), add final and abstract modifiers to classes
SLanguageId uses UUID
LangUtil created (temporary convertions between compiled and source levels of a language)
DebugRegistry supports links and properties
SRepository has a DebugRegistry

Conflicts:
	core/project/source/jetbrains/mps/project/ProjectRepository.java