[CORE] Move public resources to a /public directory

Advantages:
* Increases security by preventing direct access to file/
* We are careful and have a defined('GNUSOCIAL') || die() to prevent
  direct access to GS files, but we may miss one or a vendor/extlib may
  not be as careful
* Improves directory structure - It's more natural to physically
  separate what is public from what are GNU social resources

plugins/Directory/css/directory.css

@@ -1,60 +0,0 @@
-/* CSS file for the Directory plugin */
-
-div#profile_directory div.alpha_nav {
-    overflow: hidden;
-    width: 100%;
-    text-align: center;
-}
-
-/* XXX: this needs serious CSS foo */
-div#profile_directory div.alpha_nav > a {
-    border-left: 1px solid #000;
-    padding-left: 2px;
-}
-div#profile_directory div.alpha_nav > a.first {
-    border-left: none;
-}
-
-div#profile_directory div.alpha_nav a:link {
-    text-decoration: none;
-}
-
-div#profile_directory div.alpha_nav a:visited {
-    text-decoration: none;
-}
-div#profile_directory div.alpha_nav a:active {
-    text-decoration: none;
-}
-div#profile_directory div.alpha_nav a:hover {
-    text-decoration: underline; color: blue;
-}
-
-div#profile_directory div.alpha_nav a.current {
-    background-color:#9BB43E;
-}
-
-table.profile_list {
-    width: 100%;
-}
-
-table.profile_list tr {
-    float: none;
-}
-
-table.profie_list td {
-    width: 100%;
-    padding: 0;
-}
-
-
-th.current {
-    background-image: url(../images/control_arrow_down.gif);
-    background-repeat: no-repeat;
-    background-position: 60% 2px;
-}
-
-th.current.reverse {
-    background-image: url(../images/control_arrow_up.gif);
-    background-repeat: no-repeat;
-    background-position: 60% 2px;
-}