Remove embargo, fix several issues

[timdegroote]

• Removes the embargo functionality from the ui
• Adds a file download button to the publication detail page
• Adds a back button to the publication detail page which takes the user back to the home page

TL;DR: Fixes https://github.com/CUL-DigitalServices/avocet-ui/issues/266, https://github.com/CUL-DigitalServices/avocet-ui/issues/261 and https://github.com/CUL-DigitalServices/avocet-ui/issues/257

This can't be merged before there is a Hilary counterpart to this PR.

[timdegroote]

Assigning @ucamhal for review.

[timdegroote]

Hilary counterpart can be found at https://github.com/CUL-DigitalServices/avocet-hilary/pull/54

[ucamhal]

Also there's a typo in the commit message of e1a0f9b4e22c89d1c4d51db6afe1eb901d5a2ddf:

Pubicationfile

Also the multiline commit messages should normally have a blank line after the title/summary line. Check out http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

[timdegroote]

Thanks @ucamhal! Added some follow-up.

[ucamhal]

Thanks, merging.