adds devise to the gemfile; adds form for user signup; generates devise migration
adds user authentication in controller; adds view logic for user session on homepage
Merge branch 'master' of https://github.com/Lkroner/Snack_Overflow into devise_setup

Conflicts:
	Gemfile.lock
	db/schema.rb
Merge pull request #2 from Lkroner/devise_setup

Devise setup