remove unused classes
added a destroy action to delete
update to fix the pre render error
added showcase model
add showcases model
add exhibit quering
added devise for login.
add exhibits controllers
added tests to exhibits
add showcases controller and tests
Merge branch 'add-showcases' of https://github.com/ndlib/beehive into add-showcases

Conflicts:
	app/assets/javascripts/components/section_image.js.jsx