Added Data Citation Guide to Docs

Related to Issue #699 to help with putting in the "Why Cite?" link next
to the Data Citation in Dataverse.
Started migrating UNF documentation to Sphinx

This is just a PLACEHOLDER for now. Leonid will help review this
documentation which currently lives in thedata.org to make sure the
content is up to date and correct.
Fixing the issue where thumbnails for dataset "search cards" could be chosen from files that no longer (not yet) occurred in that
particular version of the dataset.
Added references and fixed the headings with images
Fixes for the datafile delete functionality.
Fixed layout bug in the Create Dataset Template workflow where the selectmany checkbox table was only displaying one option.
Added "Why Cite?" link to the citation block on the dataset page, that links to the data citation user guide page.
modified the internal ingest workflow so that the md5 is calculated when the file is saved in the temp location; i.e., before we attempt
to save it permanently.
Merge branch 'master' of https://github.com/IQSS/dataverse

Conflicts:
	src/main/webapp/dataset.xhtml