Execute Procs/Lambdas config vars

- Allows their use in templates
Post unicorn recipe to capistrano 3

- Rename unicorn partial template from Procfile.web to Procfile.app,
  matches role segmentation.

- Use command mapping to setup partial unicorn procfile instead of hard
  coded template
Update Capistrano dependency to latest 3.1

- Until sshkit's invoke is removed (causes conflict with rake backend)
  it's recommend that you use the hab278/sshkit fork in your gemfile
Move unicorn pidfile

- #{app}/shared/pid folder is not created by default in capistrano 3
  combined with the fact that maintaining a pidfile is not very
  useful in case of improper daemon shutdown, move unicorn pidfile to
  /tmp/unicorn.#{app}.pid
Be explicit in rake tasks dependencies
Ensure unicorn parcial procfile is '\n' terminated
Default rails_env to "production"
Correctly create symlinks for foreman logs
Properly set foreman user

- foreman_user was deprecated
Call foreman:log during deploy

- It's the end of the foreman setup chain, so it ensures every
  intermediary step is called.
Ensure Procfile-matross is recreated (or not)
Use release_path instead of current_path

- Planning to move whole setup to after deploy:update instead of
  deploy:finished
Clear actual Procfile-matross on foreman:pre_setup
Don't delete actual repository's Procfile

- Also prefer clear steps instead of clever bash tricks