Collective-editskinswitcher

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- Added menu item to set the context as a navigation root
(plone.app.layout.navigation.interfaces.INavigationRoot) guarded by
new permission "Set navigation root", by default only for Manager.
[maurits]

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- Do not show the Styles menu when there are no styles to choose.
[maurits]

- Moved PAGE_WHITE_LIST and SUFFIX_WHITE_LIST from traversal.py to new
config.py.
[maurits]

- Added SUFFIX_WHITE_LIST to avoid triggering a forced login for css
or javascript files, otherwise the login form will look ugly. Also
added logo.jpg/png/gif and favicon.ico to the PAGE_WHITE_LIST for
the same reason.
[maurits]

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- Do not force logging in when you get this header for a login page
(specified by the PAGE_WHITE_LIST).
[maurits]

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- Use ``get_header`` instead of ``get`` when looking for headers to
force logging in or force using the edit skin.
[maurits]

- Allow setting a default skin on a folder, using the new Styles
context menu.
[dreamcatcher]

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- Fix: when we need authentication and we are anonymous then we do
*not* want to switch: we want to have the default behaviour of
getting the standard skin instead of the edit skin. Added some more
inline documentation.
[maurits]

- Switch back to checking the ``__ac`` cookie to see if someone is
anonymous or not; the getSecurityManager check always says we are
anonymous, though I thought I had seen it working previously.
[maurits]

- Add logging lines for debugging.
[maurits]

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- Change the switch skin action to a multiple selection. When one
of the selected actions returns True, we switch the skin.
[maurits]

- Also accept urls like admin.example.org as edit urls.
[maurits]