Update base_list.html.twig

The additional blocks will allow adding attributes and additional classes to <table> and <th> tags without needed to make a copy the whole view. I'm interested in this because I'd like to use the FooTable.js library, which uses data attributes to set the auto-show/hide for each column (for responsive tables).

If it's of interest, I could create a pull request with the templating code that I'm adding into the <th> tags. It allows the attributes on the tag to be set per field by specifying as an option within the Admin class. I.e., 'th_attributes' => array('name' => 'value', ...)

Here's the additional code that could be included within the <th> tag: {% if field_description.options.th_attributes is defined %}{% for th_attribute, th_attribute_value in field_description.options.th_attributes %}{{ th_attribute }}={{th_attribute_value}}{% endfor %}{% endif %}
Yes, good idea. I like your name better than the one I had suggested. This is my first pull request, so I'm not sure of what happens next. If you need me to update the request to the new names then just let me know.