Add download links to the datafile display section of the dataset page

[eaquigley]

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Author Name: Leonid Andreev (@landreev)
Original Redmine Issue: 3518, https://redmine.hmdc.harvard.edu/issues/3518
Original Date: 2014-02-03
Original Assignee: Elda Sotiri

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Add download links for individual files.
Links should point to the API download calls; these will contain the combined functionality of the 3.* API data access calls and the download servlet.

[eaquigley]

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Original Redmine Comment
Author Name: Leonid Andreev (@landreev)
Original Date: 2014-02-11T16:29:58Z

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This should be working per 4.0alpha1 requirements. Once the files are uploaded and the changes saved, download links will appear next to the file names on the dataset page.
The links will NOT appear for the uploaded files until the user clicks 'save'. ("[unsaved file]" will appear instead).

[eaquigley]

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Original Redmine Comment
Author Name: Elda Sotiri (@esotiri)
Original Date: 2014-02-11T20:24:04Z

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Tested on dvn-build DVN_4_0-131

This is working as described above.