Document Detail Template Layout Adjustment

**Document Detail Template Layout Adjustment**

This pull request adjusts the document detail template layout in two ways.  First, this PR wraps the "preview" for image documents in an "a" tag.  Many potential users do not know how to "right click, save image", so this will simplify downloading the image.  Second, this PR add a "Download Document" link above "Document Metadata".  This reflects the same layout as layers and maps.