Added model user
First version of User-Management added
Further improved User Management, Added Favorites Table to Database, still needs a PDF Table to be linked with. References partially implemented.
Added personal Profile page. Users now have a Username to register with. Pending: Edit Username.
Modified login: Now requires [Username, Password] instead of [Email, Password]. Finished Register and Update, working as intended now. Usernames are now unique.
Merge branch 'User'

Conflicts:
	app/views/layouts/application.html.erb
	config/routes.rb
	db/schema.rb