init app : links
update settings.py : update INSTALLED_APPS
Link model test : should have original field
Link model test : should have shorten field
Link model test : should have unique shorten field
Link model test : save with empty shorten should have random shorten
Merge branch 'feature/modeling-links' into develop

* feature/modeling-links:
  Link model test : save with empty shorten should have random shorten
  Link model test : should have unique shorten field
  Link model test : should have shorten field
  Link model test : should have original field
  update settings.py : update INSTALLED_APPS
  init app : links