Customizable file context menu

It would be great if it was possible to define some new external commands to perform on files on a per-project basis.
A typical use-case would be to be able to execute a shell script in the folder tree on the left and see the results in the console at the bottom.
Another one would be to launch gimp when opening an image.

The best would be to be able to specify this in the project definition file such as:

{
 "file_commands": [ {
  "name": "Execute script",
  "cmd": "/bin/sh $1",
  "types": ".sh"
 }, {
  "name": "Open with Firefox",
  "cmd": "/usr/bin/firefox $1",
  "types": ".htm .html .xml"
 } ]
}