Add sync_photos command to sync LDAP photos into Socialcast

* Add `sync_photos` command
* Adds `profile_photo` mapping to `ldap.yml` which can be set to an LDAP attribute.
* extract `ldap_config` and `each_ldap_entry` shared by `provision` and `sync_photos`

![screenshot_10_3_13_2_20_pm](https://f.cloud.github.com/assets/11699/1264536/35b6ee9e-2c61-11e3-92b3-b9f8d599424c.png)