Add external IP discovery module

This module performs an HTTP request to ifconfig.me/ip.
The body of the response contains the publicly routable IP from
which the request originated. This can be useful in discovering
routes on pivoted hosts and initial recon as a simple aux module.
msftidy and module placement per todb
Apply Egypt's cleanup

Remove revision, raise the exception itself, remove scanner mixin,
datastore['RHOST'] unstead of RHOSTS, and useles agent var removed.
original modules renamed
modified CommandDispatcher::Exploit to have the change into account
avoiding grouping options
modify exploits to be compatible with the new netcat payloads
Adding Honeywell exploit.
Merge branch 'release'
Updating URL for Honewell EBI exploit
Merge branch 'external_ip_discovery' of https://github.com/sempervictus/metasploit-framework into sempervictus-external_ip_discovery
cleanup before merge external_ip
use of send_request_cgi
Merge remote-tracking branch 'jvazquez-r7/netcat_gaping' into rapid7

[Closes #1576]