Set up sane(r) defaults for the CSS <link> tag rendering.

This is slightly backwards incompatible since the media attribute no
longer is specified by default.

compress/templates/compress/css.html

-<link href="{{ url }}" rel="stylesheet" type="text/css" media="{{ media|default:"all" }}" title="{{ title|default:"all" }}" charset="utf-8" />
+<link href="{{ url }}" rel="stylesheet" type="text/css"{% if media %} media="{{ media }}"{% endif %}{% if title %} title="{{ title|default:"all" }}"{% endif %}{% if charset %} charset="{{ charset }}"{% endif %} />
\ No newline at end of file