Line numbers, nonprinting characters for File Preview

Should be self-explanatory. File preview (especially for code file formats) should have line numbers and the option (like a checkbox on the file preview and/or a user setting for a default) to display nonprinting characters such as whitespace, tabs, newlines, etc.

At least make line numbers an accessibility setting if they are too stylistically intrusive for some people (I don't know who this would be though).