Fix human-readable names of content types in permissions screen.

![screenshot 2014-12-09 18 45 58](https://cloud.githubusercontent.com/assets/54067/5370175/a97b87e2-7fd3-11e4-99dd-e1ea5f9979a2.png)

My logs were flooded with:

    Notice: Trying to get property of non-object in vinculum_ui_permission() (line 60 of sites/all/modules/vinculum/modules/vinculum_ui/vinculum_ui.module).

This gets the node type's human readable name and uses it in the permissions screen.