Indication of the subject among those allowed in Dataverse

[pablovp86]

As an author
I want to indicate the subject of the dataset during the submission
So that the dataset on Dataverse is categorized into a subject

Currently "N/A" is used as subject for all datasets published by the plugin.

For a first version, make the the list of possible subjects hard-coded, using the 14 default subjects of Dataverse.
On a next issue we can use the native API to list the subjects.

[pablovp86]

Release.