Document #2515
Fix for error when attempting to save static_placeholder on non-cms pages

Before this fix user receives:
AttributeError: 'NoneType' object has no attribute 'get_title'

When attempting to "Publish Changes" on a non-CMS page with static placeholders.

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Removed remaining plugins directory

Regarding: https://github.com/divio/django-cms/pull/2581
Merge pull request #2600 from yakky/feature/render_model_doc

Document #2515
Merge pull request #2601 from mkoistinen/statics_outside_of_cms

Fix for Publish Changes on non-cms pages containing static_placeholders
Merge pull request #2604 from Chive/feature/cleanup-plugins

Removed remaining plugins directory