Merge pull request #355 from mrvisser/paris2013-expiring-signature-utc

(Paris2013) Use Date.UTC so that the date is not created with a local GMT offset.
Simple image preview names
Added unit tests for filenames
Setting preview status to ignored for ignored items
Merge pull request #356 from simong/paris2013-simple-image-preview-names

Paris2013 simple image preview names
Merge pull request #357 from simong/paris2013-previews-ignore-links

Paris2013 previews ignore links
(Paris2013) Activities adding content previews