Added ra-icon-paperclip-tiny - works like ra-icon-magnify-tiny

This is general-purpose and not yet being used for anything, but it is a
10x10 icon of a dark grey paperclip, styled to match the existing
ra-icon-magnify-tiny which is a 10x10 icon of a dark grey magnifying
glass (which is used all over as the relationship column links). The
plan is to use this new icon for generic links to file/attachment
content...