File properties viewer

[dkastl]

Together with #543 and a #542 we could fetch and display properties of every file in a DAT archive.

There are properties already available in the metadata of a DAT archive, but additional metadata could be retrieved from remote without downloading the whole file.

Examples:

• EXIF data for images
• Thumbnail image for images
• lasinfo metadata from point cloud raw data files
• gdalinfo or ogrinfo from various spatial data files

Lots of data formats provide standardized metadata, like music or video files.