ProteinDomainComplexForm - Add PDB code and link on the page to help user find domain on PDB website

Final review step in contribution

See merge request !16

Using position:absolute was the cause of the blinking for the first render of the back of the card
Using .choices_background:hover{...background-color:white} was the cause of the impression that the flip card was turning only one out of two
Moving down box-shadow to flip-card-inner level

* remove tab
* add bigger save button to help user see and use it
* steps.count -1 to be consistent with tabs count, and tutorials

Also remove dead code

fix #232

fix #230 by creating a proper Celery chord task instead of chaining directly
from a group to a single task

WIP on #229

fix #229

FIX #229