Add a dummy_request method to Page so that we can generate page previews without passing in the active request object (which may have undesirable side effects, e.g. may be a POST)
Add get_page_modes and show_as_mode methods to Page.

This abstracts out from the preview methods the details of how the page is generated.
Support within wagtailadmin for selecting a view mode in which to preview a page.

The 'preview' option is split out from the 'save' popup menu into its own button (it was deemed appropriate to split it off since it doesn't perform any database-level actions). If the page defines multiple page modes in get_page_modes, this button becomes a popup, allowing the editor to choose a mode. Finally, preview_on_create and preview_on_edit are updated to pass the chosen mode into the page's show_as_mode method.
Removed patched treebeard from vendor folder
Updated wagtail to use treebeard 2.0
Pin django-taggit to 0.11.2
Django-taggit 0.12.x seems to break wagtail
Merge branch 'master' into treebeard-update

Conflicts:
	setup.py
Use Treebeard 2.0 add_child method
Added doc_serve signal
Add tox.ini for multi-version testing
add tox test environment for sqlite, and include elasticsearch
Python 2.6 compatibility - fixes #156
Renamed doc_serve signal to document_served
Added changelog entry for document_served signal
Merge pull request #208 from gasman/feature/tox

tox test environment and Python 2.6 support
Merge pull request #206 from kaedroho/doc-serve-signal

Added document_served signal
add changelog note re Python 2.6 compatibility
Eliminate 'patterns' from wagtailadmin/urls.py as per https://code.djangoproject.com/ticket/22218
Eliminate 'patterns' from wagtailcore/urls.py as per https://code.djangoproject.com/ticket/22218
Eliminate 'patterns' from wagtaildocs/urls.py and admin_urls.py as per https://code.djangoproject.com/ticket/22218