Recent Listings Tile for collective.covers

I added a simple tile for including recent listings from the mls into a collective.cover page. You can change its configuration in the compose view, so you can give it a custom title, add a limit parameter for the amout of listings and a relative link to the intended listing detail page. It is developed and manual tested on a Plone 4.3.3, connected to the ecuador mls.
Notes & Todo:
+  i provide some basic tests in test_tile_recent_listings.py, but was not able to run them at all. with a fresh virtualenv i get: *Error: There is a version conflict. We already have: zope.interface 4.1.0* which i couldn't resolve
+ i just tested it in a standard setup, not with local MLS Setting active
+ please review the quality of code and give feedback what needs to be improved
+ i will continue with further tiles for listing collections, a listing search mask and a updated basic listing tile
![screen shot 2014-05-15 at 19 02 12](https://cloud.githubusercontent.com/assets/3539915/2983738/05a05aec-dc29-11e3-918f-9dd87fc776bc.png)
![screen shot 2014-05-15 at 19 02 29](https://cloud.githubusercontent.com/assets/3539915/2983739/0aa63480-dc29-11e3-863f-5fb6837988f1.png)