Choose a script or excecutable file as a program

[Emiliano Dalla Verde Marcozzi]

When i click the 'Add' button, to add a new program, the 'Search' button list
all the installed applications. It would be nice if (for example) there is another
button that let me choose a file (for example a bash script, a python script,
whatever excecutable), once i select the file, the 'Command:' input has the
full path to the file i choosed.