feature 1519: admin instructions are dispatched into several tabs. Only

applied to en_UK and fr_FR. The help content itself needs some updates
but it will be another set of commits, in this commit, I nearly only
modified the container.

The new "Add Photos" help page only introduces you to 3 main ways to add
photos: direct upload, pLoader and FTP. Each of them has a dedicated tab
on the Admin>Photos>Add screen.

No use of the big question mark icon linked to the Help pages in the
administration header, to avoid having this icon twice : in the header
+ in the content next to H2.

git-svn-id: http://piwigo.org/svn/trunk@5182 68402e56-0260-453c-a942-63ccdbb3a9ee

language/en_UK/help/help_virtual_links.html

@@ -0,0 +1,12 @@
+<p>Photos are displayed in the category corresponding to the file
+directory.</p>
+
+<p>You can also display a picture in several categories, without duplicating
+the file on your web server. Associate the photo to any category from the
+photo editing screen (that any administrator can reach from the photo page
+on the gallery side).</p>
+
+<p>Virtual categories are based on this concept: they have no corresponding
+directory. Create virtual categories
+from <span class="pwgScreen">Administration &raquo; Categories &raquo;
+Manage</span>.</p>