Moved 1 list, 1 inline-table and 1 margin-collapse tests
to their better and more appropriate folders, along
with their associated reference files and/or
support image.

--HG--
rename : css21/reference/list-style-021-ref.xht => css21/lists/list-style-021-ref.xht
rename : css21/list-style-021.xht => css21/lists/list-style-021.xht
rename : css21/support/cat.png => css21/lists/support/cat.png
rename : css21/margin-collapse-015a.xht => css21/margin-padding-clear/margin-collapse-015a.xht
rename : css21/reference/inline-table-valign-002-ref.xht => css21/visudet/inline-table-valign-002-ref.xht
rename : css21/inline-table-valign-002.xht => css21/visudet/inline-table-valign-002.xht