Fix template name for django-threadedcomments compatibility hack.

Using comments/list.html now, like the pull request at
https://github.com/HonzaKral/django-threadedcomments/pull/39 provides.
setup.py: move Django from `install_requires` to `requires`
Use setuptools dependencies to specify the requirements of plugins
JS: clarify jQuery selector usage in variable naming.
Fix setuptools extras_require to install other dependencies.
Add check for `micawber` existance in `oembeditem` plugin.
JS: rename variables in `cp_tabs.js` for clarity
Fix error when content items get orphaned after switching layouts.

The Placeholder is removed, so can't save the ContentItem anymore with
the old placeholder_id.
Fix unregistering items from the old dom_placeholder on moving them.
docs: brush up installation instructions for plugins
Set version to 0.8.4
Cleanup documentation bits and typoos
Small code style fix.
docs: reorganize TOCs for better browsing experience

- Include templatetags in index
- Swap bundled/new plugins.
- Add separate TOC for API documentation
docs: set Django version to 1.3.4
docs: use extra-dependencies install method in quickstart too.
Fix 'code' plugin for Pygments 1.6rc1

Pygments 1.6rc1 defines a "reg" lexer without any descriptive name.
Bump version of django-wysiwyg_ to 0.5.1 because it fixes TinyMCE integration.
Shorten the "repr" of the code plugin
Mark render_placeholder() and render_content_items() output as safe.

Allow the content to be easily used in rendering plugins.