Open in external default program

[asiloisad]

Summary

Introduce new keyboard shortcut (e.g. alt-enter) to open selected file in external (system default) program.

Motivation

The function will be very usefull to open non-text file, which are produce in workflow. e.g. python via python-docx package can produce valid .docx file. Then you can use fuzzy-finder to find it and open in MS Word (because atom cannot deal with it).