MODE-1956 Add helper function to (un)escape illegal JCR characters

_This is superseded by an [updated pull-request](https://github.com/ModeShape/modeshape/pull/897)._

MODE-1956 Add helper function to (un)escape illegal JCR characters
MODE-1958 DDL Sequencer should use Jsr283Encoder rather than its own custom code

Added a getter in jcr.api.Session to return a class of utilities. This new class is called jcr.api.JcrUtils. Removed the code from DDL sequencer framework dealing with converting JCR-illegal characters and replaced with calls to the new JcrUtils class. The JcrUtils class has methods for encoding and decoding JCR names. The implementation of the methods just call through to the default encoder/decoder.