don't try to configure viewer related stuff if it couldn't have been created (non webGL browsers)
If the coefficient in the gl.onmousewheel function reached 0 it wasn't possible to zoom out any more (by mousewheel). Fixed this, by setting coefficient to at least 0.0005 when zooming out again.
Added Firefox as supported browsers for the WebGL error.
Get rid of the error:
Resource interpreted as Script but transferred with MIME type text/plain: "blob:null/[…]".
when loadind the workerscript by creating the Blob with "type" : "application/javascript":
Merge branch 'non_webGL_support' into gh-pages
Merge branch 'interface_improvements' into gh-pages