New Feature: Add "insert authorization header" context menu action to the header form

[GoogleCodeExporter]

This feature will provide yet another method for add a basic authorization 
header to the request. The user can right-click the request headers form and 
choose "Insert Authorization header..." which will bring up a dialog that 
allows entering a username and password (with password obscured) that will be 
base64 encoded and inserted as a Authorization basic header when the user 
clicks OK.

This advantage of this method is it provides a means of pre-authoring the 
request which doesn't require entering the username and password in plain text 
on the url.

Original issue reported on code.google.com by stephen....@gmail.com on 7 Sep 2014 at 2:53