Make attachments widget into includable html template

[atodorov]

$ grep Attachments * -R | grep -v node_modules | grep -v locale | grep Attachments
bugs/templates/bugs/get.html:                    {% trans 'Attachments' %}
templates/case/get_details_case_run.html:								Attachments
templates/plan/get.html:					<a href="#attachment" title="attachment">{% trans "Attachments" %} (<span id='attachment_count'>{% attachments_count test_plan %}</span>)</a>
testcases/templates/testcases/get.html:                    {% trans 'Attachments' %}

TP, TC and BUG use Patternfly cards, case/get_details_case_run.html is legacy but pretty much the same probably. Duplication needs to be removed, see templates/include/