Fixed {% render_plugin %} example

The instance.child_plugins reference is not correct, it should be instance.child_plugin_instances.
Merge pull request #2045 from andreiavram/patch-1

Fixed {% render_plugin %} example
Merge branch 'develop' of ssh://github.com/divio/django-cms into develop
remove relative positioning from item
this fixes additional issues with collapsable positioning saving
adds initial esc command to the modal window
workaround for the rare key error while publishing pages
Merge pull request #2108 from FinalAngel/feature/fixes

Additional Frontend Fixes
Merge remote-tracking branch 'divio/develop' into develop