Fixes issue #505: Module links in webadmin should use _blank.
Wikipedia "Icon External Link"
(http://commons.wikimedia.org/wiki/File:Icon_External_Link.png)
is being used as an icon for the external link.
Changes icon to the [File:External](https://commons.wikimedia.org/wiki/File:External.svg)
NOTICE: icon license is public domain.
Updated NOTICE file.
Move CSS definition into template file so it can be processed by template engine.
This gives us opportunity to handle URI prefixes.
Merge commit 'refs/pull/568/head' of github.com:znc/znc