Collective.documentviewer

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- Added italian translation
[keul]

- Fixed JavaScript issue on Chrome: expected global variable ``sidebar`` was not global
[keul]

- handle conflict errors in async processes better
[vangheem]

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- hide doc viewer from screen readers since they won't be able to make
sense of <img> tags for pdf pages.
[vangheem]

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- Handle errors when searching
[vangheem]

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- handle no blob found on content
[vangheem]

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- fix release

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- Handle file deleted to clean up files
[vangheem]

- fix not being able to hide sidebar
[vangheem]