Maping of union leaf a bits leaf YANG type to JAVA inner classes.

Maping of union leaf a bits leaf YANG type to JAVA inner classes.

Implements following mapping:
- YANG union leaf:
-- leaf name -> name of inner class
-- leaf types -> attributes of inner class
- YANG bits leaf:
-- leaf name -> name of inner class
-- leaf concrete bits - attributes of inner class

Bug fix:
- generation of constant list of regular expression also if no pattern in
  string YANG type is specified

Change-Id: I7c52eef34de610877c3dc0c24d44bb89015c953b
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>