add drop-shadow shorthand test
Merging PR #25 https://github.com/w3c/csswg-test/pull/25
moved to user folder, renamed files (no svg)

--HG--
rename : contributors/ttwf_tokyo/starters/svg-filters/svg-filters-ref-drop-shadow.html => contributors/ttwf_tokyo/junichikawa/filters-drop-shadow-ref.html
rename : contributors/ttwf_tokyo/starters/svg-filters/svg-filters-test-drop-shadow.html => contributors/ttwf_tokyo/junichikawa/filters-drop-shadow.html
moved to user folder, renamed files (no svg)