Add possibility to view a file as plain text

[tomas-nestorovic]

For many cases, the DOS → Show as binary (or Ctrl+B) option is a too cumbersome way to display textual files on a disk (e.g., *.BAT). At least for MS-DOS filesystem, it thus would be desirable to facilitate displaying of such files as plain text, optionally with showing also non-printable characters in some different way than other printables (similarly as done in ZX Spectrum BASIC files listing).