[Fix #1232] make the behavior of AndOr cop configurable

Currently, the AndOr cop bans the use of keywords 'and' and 'or'
completely. This patch adds a configuration option `OnlyCheckConditionals`
which when set, restricts the AndOr cop to only conditionals.
I meant this:

```
[4] pry(main)> condition, body, else_body = *Parser::CurrentRuby.parse('if something then x else y end')
=> [(send nil :something), (send nil :x), (send nil :y)]
```

By breaking up structurally the node you reveal more information to the reader of the code. And using `*` instead of `children` is more efficient in terms of performance.