Bugfix on s13admincontrols.js

s13admin.submit_form wasn't properly getting the values of the inputs
and the textareas when they initially had no content, i.e. when creating
a new section. Fixed by using .val() instead of .attr("value") or
.text() in input and textarea fields, respectively. Should be good now.

Also, added an area where feedback can be given the user after hitting
SUBMIT. Changed the behaviour of the Cancel/Close button as well. And
of course, styling changes were applied.