This moves all static webadmin files (images, css) to the data/ subdirectory
of the skin dir. The webadmin module is changed to redirect requests to
/<skin name>/ to that data directory. The skins are changed to use the
new URL when linking to their stuff. (I only needed to change the path to
the main.css file in each Header.tmpl. Since the .css and the images are now
in the same directory, relative URLs work just fine).
This means that we now generate different URLs after changing the webadmin
skins and the browser cache can do its thing.
git-svn-id: https://znc.svn.sourceforge.net/svnroot/znc/trunk@1481 726aef4b-f618-498e-8847-2d620e286838
