SSH command, verbose mode, execute option hashes

* Adds an `opsicle ssh [environment]` command to ssh to a server instance in a given stack from the terminal. Doesn't show a menu and instead auto-connects to an instance if there is only one.
* Changes `api_call` on `Client` to use `public_send`, because it should.
* Adds interrupt handling since there's a menu in a command, now. 
* Adds verbose mode flag
* All `execute` methods in commands get option hashes now, a nice way of being able to provide options (like the verbose flag above) to our own classes. Notice I use `options.__hash__` because I don't want to pass `Commander::Command::Options` objects out of the scope of Commander (dependency concerns, adds complexity, and makes RSpec annoying to stub)
* Tests, wahoo!