Progress bar on standard error.

This will add a progress bar using '.' characters, using generators to report suspicious files as they are seen. This is printed on standard error to allow easier automation.

Compare with progress bar:
```
$ python WireLurkerDetectorOSX.py
WireLurker Detector (version 1.0.0)
Copyright (c) 2014, Palo Alto Networks, Inc.

[+] Scanning for known malicious files
.................
[-] Nothing is found.
[+] Scanning for known suspicious files
..
[-] Nothing is found.
[+] Scanning for infected applications (may take minutes)
....................................................................................................................................................................................
[-] Nothing is found.
[+] Your OS X system isn't infected by the WireLurker. Thank you!
```

To without progress bar:
```shell
$ python WireLurkerDetectorOSX.py 2>/dev/null
WireLurker Detector (version 1.0.0)
Copyright (c) 2014, Palo Alto Networks, Inc.

[+] Scanning for known malicious files
[-] Nothing is found.
[+] Scanning for known suspicious files
[-] Nothing is found.
[+] Scanning for infected applications (may take minutes)
[-] Nothing is found.
[+] Your OS X system isn't infected by the WireLurker. Thank you!
```


See #11 for original pull request.