Zoomable Visual Transformation Machine

It is very useful to be able to deliver the SVG in SVGZ (i.e. compressed
with GZIP) from the server to the viewer.

I have implemented this in the GVLoader class.

It works like this:
When a HTTP request is made to read the SVG from the server, the header
"Accept-Encoding: gzip" is added. This gives the server a chance to decide
if it wants to deliver SVGZ instead of SVG. (Servers that don't deliver
SVGZ does not have to).

When the response is read, a check is made if the encoding is "gzip". If
so, a GZIPInputStream is used to filter and inflate.

In the patch, I also changed some references to static members that should
not be made via the instance.