Contact form

[Pivotal Tracker Story](https://www.pivotaltracker.com/story/show/63103292)
- added cucs, steps and view specs
- added `_contact_form.html.erb` partial and its css
- added #send_contact_form to VisitorsController
- added Mailer controller with #contact_form
- added email template mailer/contact_form
- added confirmation email + template `mailer/contact_form_confirmation` + specs
- specs for VisitorsController and MailerController
- added config to `development.rb` for sending email with gmail smtp
- added `features/support/selectors.rb` to support with_scope method
- minor refactoring in User details cucs to resole ambiguity with email field