contrib: add mco/mfw/mbn, a more interactive wrapper for mcom/mfwd/mbnc

[mineeyescyou]

This is a somewhat complicated (i.e. takes more than 5 minutes of which 4 are
for reading mans to write) script that does two things: allows aliases like in
some other mail clients, and prompts the user for addresses and subject before
launching mcom under one of its names.

There are a few reasons why I made it. Firstly, of course, to have aliases.
Secondly, to save typing when I am in interactive shell (rather than sending
mail via scripts etc.). Finally I had a problem of forgetting to specify some
important headers before that, and I doubt I am the only one. :)