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
Given what we learned from our refactoring ruby from last week and the fact that we have a mandate that we need to follow to not have more than one instance variable per controller action, you need to find a better solution for this. (Hint: Look into Presenters)