Add skipCache option to not store data in localStorage but still fetch it

I believe it would be useful to have an option to skip storing data in the local storage.

In my use case I want to fetch several scripts using basket in parallel and then store all but one.
It is needed as data is user specific, needed only for this session and defines flow of the scripts after it (some flags, etc).

Example:
```js
basket.require(
    { url: 'jquery.js' },
    { url: 'component1.js' },
    { url: 'config.specific.just.for.this.session', skipCache: true },
    { url: 'component2.which.uses.flags.from.config' }
);
```

Order of the scripts is important here. It is just perfect to store common libs and components but that config will never be used again, there is no use to store it.
I know that there is `unique` flag but it will just force overwrite everytime and I would like to skip that overhead.