Add ability to list meroku applications
Clean up unneeded Meroku::Application#path

Since we're now storing symlinks to applications in ~/.meroku, we don't
need to keep track of each application's path
[RF] extract method for calculating an app's path
Tell unicorn where to store the PID
[RF] Extract common template rendering code
Add code climate badge to README

[ci skip]
[RF] Remove hard-coded `~/.meroku` paths