'Tab content' is empty and 'Operations' is not styled when adding a tab with Ajax

Problem/Motivation

Steps to reproduce:

1. Install and enable quicktabs 7.x-3.x-dev
2. Go to admin/structure/quicktabs/add
3. Click on the 'Add tab' button at the bottom of the form
4. The table should look like screenshot 1, i.e. 'Tab content' and 'Operations' columns are properly displayed
5. Make sure that at least one of the tab titles is empty so the form won't validate
6. Click on the 'Save' button

Expected result: 'Tab content' and 'Operations' columns should still show up like on screenshot 1.

Actual result: 'Tab content' is empty and 'Operations' is not styled, as displayed on screenshot 2.

Proposed resolution

The problem is that:

• The content of 'Tab content' is updated by using $('#quicktabs-form') in the js
• The styles of 'Operations' is updated by using '#quicktabs-form' in the css
• Drupal changes the form ID from 'quicktabs-form' to 'quicktabs-form--2' when it is udpated with Ajax - see drupal_html_id()

The problem could be fixed by using a form class (.quicktabs-form) instead of the form ID (#quicktabs-form and #quicktabs-form--2).
Such solution is implemented in the patch provided at #1.

Remaining tasks

Reviews and tests are welcome.

Related Issues

The following issue might be related, though the 'Operations' column does not seem to be affected: 🐛 Content tabs chose block not showing on edit tab interface Closed: outdated