UK: code refactor: link user to submission instance, closes #264
UK: pep8: code refactor of create_instance function
UK: set required xform to instance
UK: add check for existing request object
Merge branch 'master' into 264-link-users-to-submissions

* master:
  PLD: simplify conditionals
  PLD: add missing slash in API endpoint
  UK: allow anon access to public forms, closes #215
  UK: test for anonymous user access to data endpoint
  UK: custom permissions class to allow anonymous access to public datasets
  UK: allow any access to the api
  UK: add public and ona to _reserved_usernames
  UK: implemented /data/{owner}/public api endpoint
  UK: implement /data/public api endpoint
  UK: add docs for forms /public api endpoint
  UK: refactor complex retrieve class method
  UK: implement /forms/owner/public api  endpoint
  UK: test for /forms/<owner>/public endpoint
  UK: /forms/public returns list of public forms and forms with public data
  UK: js for iphone style buttons for form and data shared buttons
UK: fix kml_export - pick user from xform and not instance
UK: fix briefcase api - pick user from xform and not instance
PLD: move fetching instances into a separate function
PLD: syntax fixes
Merge pull request #297 from onaio/264-link-users-to-submissions

Link users to submissions