Add in missing arrow images

* Images from the liferay _unstyled theme
* 13_right was missing from theme when built
* 13_left was the incorrect image; it was actually 13_right
Accordion toggle icons display correctly

The icon used (arrow 13_right) has the right icon and the down icon in the
same image, stacked vertically. When clicked, the position is changed to
show the menu is open. Previously there was no line-height specified, so
both image would be displayed when the menu was closed. Now the images
have the desired appearance.
Options icon displays correctly for borderless portlets

Previously this icon was missing from the top bar of borderless portlets.
The icon was provided by the liferay _unstyled theme, and there was a rule
inside of portlet.css that was supposed to place this icon in the toolbar,
but it had incorrect selectors (see lines 244-246 of portlet.css). This
rule fixes those selectors. Also, it overrides the rule .aui
.btn-group.open .dropdown-toggle from aui.css which was hiding the icon
when the menu was opened.