Task/ajax product edit

Bug fix: [no]
Feature addition: [no]
Backwards compatibility break: [yes]
Unit test passes: [yes]
Behat scenarios passes: [yes]
Checkstyle issues: [no]*
ChangeLog updated: [no]
Documentation PR: [link to the documentation PR if there is one]
Fixes the following jira:


In this PR :
  - refactored product completeness to make it quicker
  - added a generic method for AJAX loading of tabs
  - used this method for loading the history and completeness tab of the product edit page