Homepage sponsor admin

# Changes
 - Allows sponsors on the homepage to be updated on the homepage node (based on Partners taxonomy).
 - Adds a new image style with expected dimensions for homepage partner images & a desaturate filter.

# Example
![screen shot 2014-10-20 at 5 33 14 pm](https://cloud.githubusercontent.com/assets/583202/4709614/b939b5b4-58a0-11e4-950d-046a2a6bcacb.png)

This should make sure that `isset($wrapper->field_sponsors)` first before checking.  The fear is real: QA internationl build did not revert features and is now WSOD on

EntityMetadataWrapperException: Unknown data property field_sponsors. in EntityStructureWrapper->getPropertyInfo() (line 335 of /var/www/international.dosomething.org/releases/20141021190304/html/profiles/dosomething/modules/contrib/entity/includes/entity.wrapper.inc).