Use Git LFS to store integration test files about unblob

[kissgyorgy]

A couple of caveats:

• The full git history needs to be rewritten to track tests/integration (so it will mess up the existing git repo for everyone)
• There is a 1GB limit for free usage when using Git LFS (should be enough, but we should still not go crazy with big files)
• git LFS needs to be installed on developer machines (should not be a problem?)
• rebase for existing branches might be hard (we don't have a lot of open branches now, so it's an ideal time to covert the repo)

[qkaiser]

Let's move to LFS and we can still recreate the two branches that have open pull requests if rebasing is too difficult.

[kissgyorgy]

The LFS migration is ready, README has to be updated and we can add the big files now.

[qkaiser]

See #80