When defaulting: Only invoke bat for previews if the file is text. And support for ".gz" archives

[oliverkwebb]

modified:   preview
When a file is not recognized, Instead of attempting to show the
file as the preview, It checks the mime type for "text/*". If the file's
mime type is not in "text/*", It shows what file command designates the
file as instead. If the mime type is in "text/*", It will show the
file as the preview.

With added support for "*.gz" gzip file compression, the preview is
the output of "gzip -l" on the archive to list files in the archive

[thimc]

Thanks!