Added new simpler convertor for OO

Hi, 
I enhanced your library with a lot simpler convertor using OO. Why did i do it since we have OO converter already?
1. It is the ONLY way to make your library convert documents on Mac OS X
    - abiword for Intel is not to be found (and compiling it on Macports or elsewhere is a big PAIN)
    - gdrive has issues (table borders) --> http://goo.gl/B8B5B
    - PyUNO is broken on Mac OS (and elsewhere as I hear - http://goo.gl/3MzNm)
2. It is much more see-through code than using pyuno magic. I used "Abiword converter template"

Tested and working Mac OS 10.7 Server; Ubuntu 12.10

I order to make this all work you need to set in settings.py:
WEBODT_CONVERTER = 'webodt.converters.openofficebin.OpenOfficeBinODFConverter'
WEBODT_OOBIN_COMMAND = '/Applications/LibreOffice.app/Contents/MacOS/soffice'

Also on Mac OS it is needed to set a temp folder OUTSIDE /var e.g.
WEBODT_TMP_DIR = "/Users/kosta/git/my_project/resources/tmp_webodt"
(OO has problems with rights)