Make the location of the style files to be configurable

[flint]

Hello notebook developers,

I'm working on the style of the notebook for a site installation and
would like to be able to easily switch between different styles. Of
course, I could replace the css files by others. But I think it would
be easier to change the value of an environment variable defining the
location the style files are loaded from. So I suggest to add the
following functionality to sage notebook: If a certain environment
variable is defined then its value is taken as the location the style
files are loaded from. Otherwise they are loaded from a default
location as before.
If this sounds useful to you, please have a look at my ticket #11106
on the trac server
http://trac.sagemath.org/sage_trac/
There you can download a patch which installs this feature.

Best regards,

Flint