Created admin interface to create new category

* Dashboard admin view uses _category partial
* Added validations for location and category models
* Deleted duplicate sign-in/sign-out links in layout
* Modified category index view to delete create category form section
We want to show all of our categories for each location so there aren't any location-specific categories.  To do this we are using the category partial to fill in the categories when we load the location views and as a result I wanted the location show to be aware of all of our categories.  I'm guessing the Presenter hint you gave me may help me with this issue.