[#320] Press enter should submit form just like clicking the primary sub...

...mit button

The context is the dataset creation wizard (see #320).

One of the things I did was change the wizard clickable steps from `<button>` to `<a>` because I thought that it would make more sense semantically speaking. I also added "type=button" to the others `<button>` to avoid the submit when the user hits enter because it comes first than the primary (blue) one.

For each of those elements, I added the data-* attribute to store the name and value.
I retrieve the data and add the a input hidden when user clicks on one of them.

Feel free to ask or suggest any modification.

Best,
Vítor Avelino.