Enable soft livereload of CSS and images

Prior to this commit a dummy JavaScript filename was sent to LiveReload when changing a static file (CSS, image etc.), forcing a full browser reload of the page.

This commit fixes this by sending the relative file path of the changed static resource, enabling partial live reloading for CSS- and image-changes. If more than one static file happens to end up in the same changeevent-batch, it will fall back to do a full refresh. To enable this logic, the change events with names ending with ".goutputstream*" is now filtered out as temporary.

Changes in dynamic content behaves like before.

Issue #490