Import plugin snow

Import from branch "master" of git://anongit.compiz.org/fusion/plugins-unsupported

Commit:    bfac20ca68b268151686bc1534c57aecbc0c20d0
Port plugin snow to fusilli

Add images/snowflake.png from repo
git://anongit.compiz.org/fusion/plugins-unsupported (branch master)

Commit:    bfac20ca68b268151686bc1534c57aecbc0c20d0