allow execution with a different perl interpreter

[szabgab]

Allow the user to configure the perl() that is used for execution of programs (or that is used to install modules for the application being written).

[szabgab]

the user should be able to configure one executer for each mime-type (or maybe more executers with one being the default ?) e.g. for HTML several available browsers ?
For perl 6 or python or php several implementations ?

[zenogantner]

Besides that, there should be a default executer that just interprets the hashbang at the beginning, e.g.

#!/usr/bin/perl

or

#!/usr/bin/python

[SvenDowideit]

this is a bit related to a change I made to Document::Perl::get_command - where I added getting the args from the hashbang

I would like to change that function to return a hash of the component parts so that they can be displayed and modified for #1464 - debug options dialog