initial commit for yang UI

/app/yangui - main app module folder (module console.yangui)
/common/yangutils - module with logic and utility functions (module common.yangUtils)
/assets/yang2xml - temorary xml files generated from yang modules from
controller
/assets/views/yangui - views from yang UI application used in ng-include
directive

- modified main.less: included yangui.less
- modified Gruntfile.js: changed task build_assets to build_app_assets
  on change of assets directorty as former did not existed and caused error when building
- updated locale.json

Change-Id: I706759a18bd3369cd6141f0fa859c71378ba13ad
Signed-off-by: Juraj Sebin <jsebin@cisco.com>