Upgrade yangtools from Beryllium to Boron

The YangIDE codebase is using internal artifacts of the Beryllium version of Yangtools (although this wasn't immediately obvious). The references to the Beryllium interfaces need to be replaced with the interfaces provided by Boron.

The final Boron release of YangIDE went out this way, because there wasn't enough time to determine the proper changes to make this happen before the release went final.

This set of changes needs to happen to allow for the eventual upgrade to the Yang 1.1 specification, and likely the use of the v2 binding framework.

Obviously, this change isn't as simple as just changing the version number of the artifact and fixing a couple of compile errors. A thorough analysis has to be done to understand the Yangtools interfaces that are currently being used, to plan a migration path to use the latest Yangtools.