Initial implementation of user access request to projects

app/controllers/projects/project_members_controller.rb

app/helpers/projects_helper.rb

app/mailers/emails/projects.rb

app/models/ability.rb

app/models/member.rb

app/models/members/project_member.rb

app/models/project_team.rb

app/services/notification_service.rb

app/views/layouts/nav/_project.html.haml

...ws/notify/project_request_access_accepted_email.html.haml

...ews/notify/project_request_access_accepted_email.text.erb

...iews/notify/project_request_access_denied_email.html.haml

...views/notify/project_request_access_denied_email.text.erb

app/views/projects/project_members/_pending.html.haml

app/views/projects/project_members/_project_member.html.haml

app/views/projects/project_members/index.html.haml

config/routes.rb

db/migrate/20160314114439_add_membership_request.rb

db/schema.rb