[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.
`EnforcedStyle` is guaranteed to have a value (from `default.yml` or overridden) when the cop runs in real execution, so this context is unnecessary. Move the examples to the `always` context.