Add local option for wsse_auth and wsse_timestamp

Fixes https://github.com/savonrb/savon/issues/575

I've also added `wsse_timestamp` in addition to `wsse_auth` as I think they logically fit together.

Because of the use of a splat for the `wsse_timestamp` argument, regardless of its setting of `true` or `false`, it will always generate a timestamp (since `@wsse_timestamp` is set to an Array). Should we be able to override a global `wsse_timestamp: true` with a local `locals.wsse_timestamp(false)` to not output the timestamp header?