Ftw.slider

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- New option on the slider planes allows to render the title of the pane
without the need of adding a slider pane text. Until now the title was only
rendered when the pane had some text.
[mbaechtold]

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- Fix internal url concatenation: support path with or without leading slash.
[mathias.leimgruber]

- Fix borderradius of slider button.
[Kevin Bieri]

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- Replace plone.formwidget.contenttree with ftw.referencewidget.
[mathias.leimgruber]

- Remove ftw.contentpage test dependency and everything related to ftw.contentpage.
ftw.contentpage is deprecated and is replaced by ftw.simplelaylout.
This functionality is now implemented in ftw.sliderblock.
[mathias.leimgruber]

- Add browser pane redirect view, which behaves like the one from links.
[mathias.leimgruber]

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- Update onegovtheme syling since slider update.
[Kevin Bieri]

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- Let Site Administrator add panes on site root. [jone]

- Use image cropping for sliderblock images to keep the ratio for different images.
[Kevin Bieri]

- Add compatibility for ftw.slider using new initialisation syntax.
[Kevin Bieri]

- Add compatibility for Plone sites not using ftw.theming.
Attention: These styling changes are not backwards compatible with exising Plone sites using ftw.theming.
[Kevin Bieri]

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- Update slick to 1.5.9.
[Kevin Bieri]