Add Cache-Control response header

[browniebroke]

The Thumbor version used to have this client side caching, would be nice to have it again.

Relates to #107

Description of changes:

Adding the cache-control header to the response like it used to be before v4

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[ericquinones]

Hi there,
Thank you for the contribution. I can confirm that adding the Cache-Control header is on our list to be evaluated in a future release. Please continue to monitor the repo for updates.

[karensg]

I definitely think this should be merged.

[beomseoklee]

Thanks for your effort here, @browniebroke
We have updated our solution, and your pull request has been merged into our master branch. However, as we've merged many pull requests at this time, the source code might not exactly same as what you've done. In addition, due to our internal process, we've merged source code manually, so please understand how your effort has been merged.

You can refer to the recent changes here