Added support to generate interfaces from Choices and Cases.

Added implementation to support generation of generated types from Choice and Case schema nodes from yang models into BindingGeneratorImpl;
Added test case and test files for test of generation of Generated Types;

Fixed bug in GeneratorUtil when imports were generated wrongly if the name of type was same as the name of interface/class.

Signed-off-by: Lukas Sedlak <lsedlak@cisco.com>