Support for download files as zip archive

[garcia-jj]

Closes #802. Allow users to return files as compressed zip archives.

Right now we are in freezing time until next final release, so I think this pull request can be merged only before final release.

[Turini]

sounds nice, thanks! it'd be nice some docs about it :)

[garcia-jj]

Some limitations for this component:

• Files are compressed on the fly. So we can't return the final zip file size. Download bar in browser can't calculate download time.
• Too large files like many gigabytes can throws an OutOfMemory because we don't flush the stream. I don't know if we can take care with this case, because sounds too fancy compress these kind of files on the fly.
• Compression level is the default. We need to expose some method to allow users to override then? For me sounds like unnecessary.
• In the DownloadBuilder, methods like setContentType are exposed, but without any effect. Due we can't reduce method visibility in child classes, we are only ignoring the method if called.

[garcia-jj]

@Turini docs added. Sorry if has errors, I'm editing in web mobile editor.

[Turini]

sounds great! Since this is just the builder and docs, I think we can merge before the
final... can you just replace REPLACE_ME_ON_NEXT_RELEASE for 4.1 before merging? tks

[garcia-jj]

Done. Thank you.