Default Environment Via Config

[russellballestrini]

modified:   app/models/environment.rb
modified:   app/models/repository.rb
modified:   app/views/messages/environments.text.erb
modified:   lib/slashdeploy/config.rb
modified:   spec/features/commands_spec.rb
modified:   spec/models/environment_spec.rb
modified:   spec/models/repository_spec.rb