Update the add dataset form with the fields that are going to be required

[mkalish]

The add dataset form is quite lengthy and slightly duplicative. We would like to narrow down the set of fields that users need to fill out when they create a new dataset

Tasks:

• Decide on a list of which fields should be made required
• Present the fields to the team (can just be on slack) so we can have a quick discussion
• Override the existing ckan template with one that only displays the fields we care about
• Make all the fields in the new template required