Collective-document-hide-summary

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- update add-on description
[tkimnguyen]

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- add views "Hide Title" and "Hide Title and Summary"
[tkimnguyen]

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- Fix PyPi trove classifier
[tkimnguyen]

- Add warning about deactivating or removing the add-on, and how to
fix pages that were set to use the Hide Summary view.
[tkimnguyen]

- Initial release.
[tkimnguyen]