Append immediate execution to start action

This PR improves **Start** action for immediate execution and append **Schedule** action to avoid it.

Ref. threefunkymonkeys/crocodile#3
None. Sorry, I was not thinking about backward compatibility rather than a syntactic improvement, but I should add an "alias_method" to keep compatibility.
I intended just to have a more semantic syntax when using "one run only" method, as I could use it when starting a job that need to run over the next 6 months, which could be written like this:

*given today is 07/24/2014*

```
def one_run_only
  Date.today < Date.parse("01/24/2015")
end
```

I thought it'd be more semantic like this:
```
def dismiss?
  Date.today < Date.parse("01/24/2015")
end
```

So, I could revert interface change at all or add an alias_method to maintain compatibility with or without deprecation message. Please tell me which one you think is the best. 
Sorry again, I forgot previous implementations.