Reconstruct app's structure
create  user model  & test
create sign-up form & test
create sessions controller
create test for sign-in page
implemented sign-in page
implemented sign-up-in-out page
Updated gitignore
Merge branch 'master' into TrafficInformation

Conflicts:
	Gemfile
	Gemfile.lock
	app/assets/javascripts/application.js
	app/assets/stylesheets/custom-css.css
	app/controllers/welcome_controller.rb
	app/views/layouts/_left_slidebar.html.erb
	app/views/layouts/application.html.erb
	app/views/welcome/map.html.erb
	config/routes.rb
	coverage/.last_run.json
	db/schema.rb
Updated login method