re-add IProperty and PropertyProxy
replace occurrences of org.hibernate.mapping.Property by org.jboss.tools.hibernate.spi.IProperty
fix failing tests
move IOverrideRepository to plugin org.jboss.tools.hibernate.spi
move all remaining interfaces to the org.jboss.tools.hibernate.spi plugin, update the plugin dependencies
add the missing *Proxy classes to plugin org.jboss.tools.hibernate3_6